diff --git a/README.rdoc b/README.rdoc
index 9038311c..35465f45 100644
--- a/README.rdoc
+++ b/README.rdoc
@@ -175,14 +175,14 @@ becomes:
         :text-decoration underline
 
 Pretty nice, no? Well, it gets better.
-One of the main complaints against CSS is that it doesn't allow constants.
+One of the main complaints against CSS is that it doesn't allow variables.
 What if have a color or a width you re-use all the time?
 In CSS, you just have to re-type it each time,
 which is a nightmare when you decide to change it later.
 Not so for Sass!
-You can use the "!" character to set constants.
+You can use the "!" character to set variables.
 Then, if you put "=" after your attribute name,
-you can set it to a constant.
+you can set it to a variable.
 For example:
 
   !note_bg= #55aaff
@@ -205,7 +205,7 @@ becomes:
       width: 5em;
       background-color: #55aaff; }
 
-You can even do simple arithmetic operations with constants,
+You can even do simple arithmetic operations with variables,
 adding numbers and even colors together:
 
   !main_bg= #46ar12
@@ -227,7 +227,7 @@ becomes:
       background-color: #79d645;
       width: 15em; }
 
-Taking the idea of constants a bit further are mixins.
+Taking the idea of variables a bit further are mixins.
 These let you group whole swathes of CSS attributes into a single
 directive and then include those anywhere you want:
 
diff --git a/TODO b/TODO
index 36cef6d9..05fd4c9e 100644
--- a/TODO
+++ b/TODO
@@ -2,7 +2,7 @@ Testing:
   Test html2haml and css2sass
 
 Features:
-  Sass should throw generic errors for undefined constants, not syntax errors
+  Sass should throw generic errors for undefined variables, not syntax errors
   Sass::Plugin should log errors
   There should be a way to make Haml tags not insert whitespace
   "%li, %a"?
diff --git a/lib/sass.rb b/lib/sass.rb
index e3e46ce5..fc6c3e77 100644
--- a/lib/sass.rb
+++ b/lib/sass.rb
@@ -481,7 +481,7 @@ $LOAD_PATH << dir unless $LOAD_PATH.include?(dir)
 #
 # === Functions
 #
-# SassScript defines some useful functions (see Sass::Constant::Functions)
+# SassScript defines some useful functions (see Sass::Script::Functions)
 # that are called using the normal CSS function syntax:
 #
 #   p
diff --git a/lib/sass/constant.rb b/lib/sass/constant.rb
deleted file mode 100644
index efbeb89c..00000000
--- a/lib/sass/constant.rb
+++ /dev/null
@@ -1,37 +0,0 @@
-require 'strscan'
-require 'sass/constant/funcall'
-require 'sass/constant/operation'
-require 'sass/constant/literal'
-require 'sass/constant/parser'
-
-module Sass
-  # This module contains various constant-script related functionality.
-  module Constant
-    # :stopdoc:
-    # The character that begins a constant.
-    CONSTANT_CHAR = ?!
-
-    # The regular expression used to parse constants
-    MATCH = /^!(\w+)\s*((?:\|\|)?=)\s*(.+)/
-
-    # The regular expression used to validate constants without matching
-    VALIDATE = /^!\w+$/
-
-    def self.resolve(*args)
-      parse(*args).to_s
-    end
-
-    def self.parse(value, constants, line)
-      Parser.parse(value, constants).perform
-    rescue Sass::SyntaxError => e
-      if e.message == "Constant arithmetic error"
-        e.instance_eval do
-          @message += ": #{value.dump}."
-        end
-      end
-      e.sass_line = line
-      raise e
-    end
-    # :startdoc:
-  end
-end
diff --git a/lib/sass/constant/literal.rb b/lib/sass/constant/literal.rb
deleted file mode 100644
index f99eb4ad..00000000
--- a/lib/sass/constant/literal.rb
+++ /dev/null
@@ -1,61 +0,0 @@
-# :stopdoc:
-# Let the subclasses see the superclass
-module Sass::Constant; class Literal; end; end;
-# :startdoc:
-
-require 'sass/constant/string'
-require 'sass/constant/number'
-require 'sass/constant/color'
-require 'sass/constant/bool'
-
-class Sass::Constant::Literal # :nodoc:
-  attr_reader :value
-
-  def initialize(value = nil)
-    @value = value
-  end
-
-  def perform
-    self
-  end
-
-  def and(other)
-    to_bool ? other : self
-  end
-
-  def or(other)
-    to_bool ? self : other
-  end
-
-  def eq(other)
-    Sass::Constant::Bool.new(self.class == other.class && self.value == other.value)
-  end
-
-  def neq(other)
-    Sass::Constant::Bool.new(!eq(other).to_bool)
-  end
-
-  def unary_not
-    Sass::Constant::Bool.new(!to_bool)
-  end
-
-  def concat(other)
-    Sass::Constant::String.new("#{self.to_s} #{other.to_s}")
-  end
-
-  def comma(other)
-    Sass::Constant::String.new("#{self.to_s}, #{other.to_s}")
-  end
-
-  def inspect
-    value.inspect
-  end
-
-  def to_bool
-    true
-  end
-
-  def to_i
-    raise SyntaxError.new("#{value.dump} is not an integer.")
-  end
-end
diff --git a/lib/sass/constant/string.rb b/lib/sass/constant/string.rb
deleted file mode 100644
index b358802c..00000000
--- a/lib/sass/constant/string.rb
+++ /dev/null
@@ -1,33 +0,0 @@
-require 'sass/constant/literal'
-
-module Sass::Constant
-  class String < Literal # :nodoc:
-    def plus(other)
-      Sass::Constant::String.new(self.to_s + other.to_s)
-    end
-
-    def minus(other)
-      Sass::Constant::String.new("#{self.to_s}-#{other.to_s}")
-    end
-
-    def unary_minus
-      Sass::Constant::String.new("-#{self.to_s}")
-    end
-
-    def div(other)
-      Sass::Constant::String.new("#{self.to_s}/#{other.to_s}")
-    end
-
-    def unary_div
-      Sass::Constant::String.new("/#{self.to_s}")
-    end
-
-    def funcall(other)
-      Sass::Constant::String.new("#{self.to_s}(#{other.to_s})")
-    end
-
-    def to_s
-      @value
-    end
-  end
-end
diff --git a/lib/sass/engine.rb b/lib/sass/engine.rb
index 42cdbb8d..1d1997a4 100644
--- a/lib/sass/engine.rb
+++ b/lib/sass/engine.rb
@@ -6,7 +6,7 @@ require 'sass/tree/rule_node'
 require 'sass/tree/comment_node'
 require 'sass/tree/attr_node'
 require 'sass/tree/directive_node'
-require 'sass/constant'
+require 'sass/script'
 require 'sass/error'
 require 'haml/shared'
 
@@ -27,7 +27,7 @@ module Sass
     ATTRIBUTE_CHAR  = ?:
 
     # The character that designates that
-    # an attribute should be assigned to the result of constant arithmetic.
+    # an attribute should be assigned to a SassScript expression.
     SCRIPT_CHAR     = ?=
 
     # The character that designates the beginning of a comment,
@@ -83,7 +83,7 @@ module Sass
         :load_paths => ['.']
       }.merge! options
       @template = template
-      @constants = {"important" => Constant::String.new("!important")}
+      @environment = {"important" => Script::String.new("!important")}
       @mixins = {}
     end
 
@@ -104,8 +104,8 @@ module Sass
 
     protected
 
-    def constants
-      @constants
+    def environment
+      @environment
     end
 
     def mixins
@@ -171,7 +171,7 @@ END
       @line = line.index
       node = parse_line(line, root)
 
-      # Node is a symbol if it's non-outputting, like a constant assignment,
+      # Node is a symbol if it's non-outputting, like a variable assignment,
       # or an array if it's a group of nodes to add
       return node unless node.is_a? Tree::Node
 
@@ -219,8 +219,8 @@ END
     def validate_and_append_child(parent, child, line, root)
       unless root
         case child
-        when :constant
-          raise SyntaxError.new("Constants may only be declared at the root of a document.", line.index)
+        when :variable
+          raise SyntaxError.new("Variables may only be declared at the root of a document.", line.index)
         when :mixin
           raise SyntaxError.new("Mixins may only be defined at the root of a document.", line.index)
         when Tree::DirectiveNode
@@ -240,8 +240,8 @@ END
       case line.text[0]
       when ATTRIBUTE_CHAR
         parse_attribute(line.text, ATTRIBUTE)
-      when Constant::CONSTANT_CHAR
-        parse_constant(line)
+      when Script::VARIABLE_CHAR
+        parse_variable(line)
       when COMMENT_CHAR
         parse_comment(line.text)
       when DIRECTIVE_CHAR
@@ -281,25 +281,25 @@ END
       end
 
       if eq.strip[0] == SCRIPT_CHAR
-        value = Sass::Constant.resolve(value, @constants, @line)
+        value = Script.resolve(value, @environment, @line)
       end
 
       Tree::AttrNode.new(interpolate(name), interpolate(value), @options)
     end
 
-    def parse_constant(line)
-      name, op, value = line.text.scan(Sass::Constant::MATCH)[0]
-      raise SyntaxError.new("Illegal nesting: Nothing may be nested beneath constants.", @line + 1) unless line.children.empty?
-      raise SyntaxError.new("Invalid constant: \"#{line.text}\".", @line) unless name && value
+    def parse_variable(line)
+      name, op, value = line.text.scan(Script::MATCH)[0]
+      raise SyntaxError.new("Illegal nesting: Nothing may be nested beneath variable declarations.", @line + 1) unless line.children.empty?
+      raise SyntaxError.new("Invalid variable: \"#{line.text}\".", @line) unless name && value
 
-      constant = Sass::Constant.parse(value, @constants, @line)
+      var = Script.parse(value, @environment, @line)
       if op == '||='
-        @constants[name] ||= constant
+        @environment[name] ||= var
       else
-        @constants[name] = constant
+        @environment[name] = var
       end
 
-      :constant
+      :variable
     end
 
     def parse_comment(line)
@@ -332,7 +332,7 @@ END
     end
 
     def parse_if(line, root, text)
-      if Sass::Constant.parse(text, @constants, line.index).to_bool
+      if Script.parse(text, @environment, line.index).to_bool
         append_children([], line.children, root)
       else
         []
@@ -344,7 +344,7 @@ END
 
       if var.nil? # scan failed, try to figure out why for error message
         if text !~ /^[^\s]+/
-          expected = "constant name"
+          expected = "variable name"
         elsif text !~ /^[^\s]+\s+from\s+.+/
           expected = "'from <expr>'"
         else
@@ -352,25 +352,25 @@ END
         end
         raise SyntaxError.new("Invalid for directive '@for #{text}': expected #{expected}.", @line)
       end
-      raise SyntaxError.new("Invalid constant \"#{var}\".", @line) unless var =~ Constant::VALIDATE
+      raise SyntaxError.new("Invalid variable \"#{var}\".", @line) unless var =~ Script::VALIDATE
 
-      from = Sass::Constant.parse(from_expr, @constants, @line).to_i
-      to = Sass::Constant.parse(to_expr, @constants, @line).to_i
+      from = Script.parse(from_expr, @environment, @line).to_i
+      to = Script.parse(to_expr, @environment, @line).to_i
       range = Range.new(from, to, to_name == 'to')
 
       tree = []
-      old_constants = @constants.dup
+      old_env = @environment.dup
       for i in range
-        @constants[var[1..-1]] = Constant::Number.new(i)
+        @environment[var[1..-1]] = Script::Number.new(i)
         append_children(tree, line.children, root)
       end
-      @constants = old_constants
+      @environment = old_env
       tree
     end
 
     def parse_while(line, root, text)
       tree = []
-      while Sass::Constant.parse(text, @constants, line.index).to_bool
+      while Script.parse(text, @environment, line.index).to_bool
         append_children(tree, line.children, root)
       end
       tree
@@ -394,15 +394,15 @@ END
       required_arg_count = 0
       args.map! do |arg|
         raise SyntaxError.new("Mixin arguments can't be empty.", @line) if arg.empty? || arg == "!"
-        unless arg[0] == Constant::CONSTANT_CHAR
+        unless arg[0] == Script::VARIABLE_CHAR
           raise SyntaxError.new("Mixin argument \"#{arg}\" must begin with an exclamation point (!).", @line)
         end
         arg, default = arg.split(/\s*=\s*/, 2)
         required_arg_count += 1 unless default
         default_arg_found ||= default
-        raise SyntaxError.new("Invalid constant \"#{arg}\".", @line) unless arg =~ Constant::VALIDATE
+        raise SyntaxError.new("Invalid variable \"#{arg}\".", @line) unless arg =~ Script::VALIDATE
         raise SyntaxError.new("Required arguments must not follow optional arguments \"#{arg}\".", @line) if default_arg_found && !default
-        default = Sass::Constant.parse(default, @constants, @line) if default
+        default = Script.parse(default, @environment, @line) if default
         { :name => arg[1..-1], :default_value => default }
       end
       mixin = @mixins[name] = Mixin.new(args, line.children)
@@ -422,19 +422,19 @@ Mixin #{name} takes #{mixin.args.size} argument#{'s' if mixin.args.size != 1}
  but #{args.size} #{args.size == 1 ? 'was' : 'were'} passed.
 END
 
-      old_constants = @constants.dup
-      mixin.args.zip(args).inject(@constants) do |constants, (arg, value)|
-        constants[arg[:name]] = if value
-                                  Sass::Constant.parse(value, old_constants, @line)
-                                else
-                                  arg[:default_value]
-                                end
-        raise SyntaxError.new("Mixin #{name} is missing parameter ##{mixin.args.index(arg)+1} (#{arg[:name]}).") unless constants[arg[:name]]
-        constants
+      old_env = @environment.dup
+      mixin.args.zip(args).inject(@environment) do |env, (arg, value)|
+        env[arg[:name]] = if value
+                            Script.parse(value, old_env, @line)
+                          else
+                            arg[:default_value]
+                          end
+        raise SyntaxError.new("Mixin #{name} is missing parameter ##{mixin.args.index(arg)+1} (#{arg[:name]}).") unless env[arg[:name]]
+        env
       end
 
       tree = append_children([], mixin.tree, root)
-      @constants = old_constants
+      @environment = old_env
       tree
     end
 
@@ -448,7 +448,7 @@ END
         if escapes % 2 == 1
           str << '#{'
         else
-          str << Sass::Constant.resolve(balance(scan, ?{, ?}, 1)[0][0...-1], @constants, @line)
+          str << Script.resolve(balance(scan, ?{, ?}, 1)[0][0...-1], @environment, @line)
         end
       end
 
@@ -495,7 +495,7 @@ END
             engine = Sass::Engine.new(file.read, new_options)
           end
 
-          engine.constants.merge! @constants
+          engine.environment.merge! @environment
           engine.mixins.merge! @mixins
 
           begin
@@ -505,7 +505,7 @@ END
             raise err
           end
           nodes += root.children
-          @constants = engine.constants
+          @environment = engine.environment
           @mixins = engine.mixins
         end
       end
diff --git a/lib/sass/script.rb b/lib/sass/script.rb
new file mode 100644
index 00000000..3afbb30b
--- /dev/null
+++ b/lib/sass/script.rb
@@ -0,0 +1,37 @@
+require 'strscan'
+require 'sass/script/funcall'
+require 'sass/script/operation'
+require 'sass/script/literal'
+require 'sass/script/parser'
+
+module Sass
+  # This module contains various SassScript-related functionality.
+  module Script
+    # :stopdoc:
+    # The character that begins a variable.
+    VARIABLE_CHAR = ?!
+
+    # The regular expression used to parse variables
+    MATCH = /^!(\w+)\s*((?:\|\|)?=)\s*(.+)/
+
+    # The regular expression used to validate variables without matching
+    VALIDATE = /^!\w+$/
+
+    def self.resolve(*args)
+      parse(*args).to_s
+    end
+
+    def self.parse(value, environment, line)
+      Parser.parse(value, environment).perform
+    rescue Sass::SyntaxError => e
+      if e.message == "SassScript error"
+        e.instance_eval do
+          @message += ": #{value.dump}."
+        end
+      end
+      e.sass_line = line
+      raise e
+    end
+    # :startdoc:
+  end
+end
diff --git a/lib/sass/constant/bool.rb b/lib/sass/script/bool.rb
similarity index 69%
rename from lib/sass/constant/bool.rb
rename to lib/sass/script/bool.rb
index e83a7adb..103a1be1 100644
--- a/lib/sass/constant/bool.rb
+++ b/lib/sass/script/bool.rb
@@ -1,6 +1,6 @@
-require 'sass/constant/literal'
+require 'sass/script/literal'
 
-module Sass::Constant
+module Sass::Script
   class Bool < Literal # :nodoc:
     def to_s
       @value.to_s
diff --git a/lib/sass/constant/color.rb b/lib/sass/script/color.rb
similarity index 84%
rename from lib/sass/constant/color.rb
rename to lib/sass/script/color.rb
index 89b2b883..9244624c 100644
--- a/lib/sass/constant/color.rb
+++ b/lib/sass/script/color.rb
@@ -1,6 +1,6 @@
-require 'sass/constant/literal'
+require 'sass/script/literal'
 
-module Sass::Constant
+module Sass::Script
   class Color < Literal # :nodoc:
 
     HTML4_COLORS = {
@@ -27,15 +27,15 @@ module Sass::Constant
     end
 
     def plus(other)
-      if other.is_a? Sass::Constant::String
-        Sass::Constant::String.new(self.to_s + other.to_s)
+      if other.is_a? Sass::Script::String
+        Sass::Script::String.new(self.to_s + other.to_s)
       else
         piecewise(other, :+)
       end
     end
 
     def minus(other)
-      if other.is_a? Sass::Constant::String
+      if other.is_a? Sass::Script::String
         raise NoMethodError.new(nil, :minus)
       else
         piecewise(other, :-)
@@ -43,7 +43,7 @@ module Sass::Constant
     end
 
     def times(other)
-      if other.is_a? Sass::Constant::String
+      if other.is_a? Sass::Script::String
         raise NoMethodError.new(nil, :times)
       else
         piecewise(other, :*)
@@ -51,7 +51,7 @@ module Sass::Constant
     end
 
     def div(other)
-      if other.is_a? Sass::Constant::String
+      if other.is_a? Sass::Script::String
         raise NoMethodError.new(nil, :div)
       else
         piecewise(other, :/)
@@ -59,7 +59,7 @@ module Sass::Constant
     end
 
     def mod(other)
-      if other.is_a? Sass::Constant::String
+      if other.is_a? Sass::Script::String
         raise NoMethodError.new(nil, :mod)
       else
         piecewise(other, :%)
diff --git a/lib/sass/constant/funcall.rb b/lib/sass/script/funcall.rb
similarity index 87%
rename from lib/sass/constant/funcall.rb
rename to lib/sass/script/funcall.rb
index 5b03a94b..0a60a730 100644
--- a/lib/sass/constant/funcall.rb
+++ b/lib/sass/script/funcall.rb
@@ -1,5 +1,5 @@
 module Sass
-  module Constant
+  module Script
     class Funcall
       attr_reader :name, :args
 
@@ -18,7 +18,7 @@ module Sass
 
       def perform
         unless Functions.public_instance_methods.include?(name) && name !~ /^__/
-          return Constant::String.new("#{name}(#{args.join(', ')})")
+          return Script::String.new("#{name}(#{args.join(', ')})")
         end
 
         return Functions.send(name, *args)
diff --git a/lib/sass/constant/functions.rb b/lib/sass/script/functions.rb
similarity index 79%
rename from lib/sass/constant/functions.rb
rename to lib/sass/script/functions.rb
index de29dee3..4f0f1407 100644
--- a/lib/sass/constant/functions.rb
+++ b/lib/sass/script/functions.rb
@@ -1,14 +1,14 @@
-module Sass::Constant
-  # Methods in this module are accessible from the Sass constant context.
+module Sass::Script
+  # Methods in this module are accessible from the Sass script context.
   # For example, you can write
   #
   #   color = hsl(120, 100%, 50%)
   #
-  # and it will call Sass::Constant::Functions#hsl.
+  # and it will call Sass::Script::Functions#hsl.
   #
   # You can add your own functions to this module,
   # but there are a few things to keep in mind.
-  # First of all, the arguments passed are (currently undocumented) Sass::Constant::Literal objects,
+  # First of all, the arguments passed are (currently undocumented) Sass::Script::Literal objects,
   # Literal objects are also the expected return values.
   #
   # Second, making Ruby functions accessible from Sass introduces the temptation
@@ -22,7 +22,7 @@ module Sass::Constant
     instance_methods.each { |m| undef_method m unless m =~ /^__/ }
     extend self
 
-    # Creates a Sass::Constant::Color object from hue, saturation, and lightness.
+    # Creates a Sass::Script::Color object from hue, saturation, and lightness.
     # As per the CSS3 spec (http://www.w3.org/TR/css3-color/#hsl-color),
     # hue is in degrees,
     # and saturation and lightness are percentages.
@@ -41,11 +41,11 @@ module Sass::Constant
     end
 
     def percentage(value)
-      value = value.perform if value.is_a?(Sass::Constant::Operation)
-      unless value.is_a?(Sass::Constant::Number) && value.unitless?
+      value = value.perform if value.is_a?(Sass::Script::Operation)
+      unless value.is_a?(Sass::Script::Number) && value.unitless?
         raise ArgumentError.new("Value is not a unitless number")
       end
-      Sass::Constant::Number.new(value.value * 100, '%')
+      Sass::Script::Number.new(value.value * 100, '%')
     end
 
     private
diff --git a/lib/sass/constant/lexer.rb b/lib/sass/script/lexer.rb
similarity index 88%
rename from lib/sass/constant/lexer.rb
rename to lib/sass/script/lexer.rb
index 14cd0010..fab1ceb3 100644
--- a/lib/sass/constant/lexer.rb
+++ b/lib/sass/script/lexer.rb
@@ -1,7 +1,7 @@
 require 'strscan'
 
 module Sass
-  module Constant
+  module Script
     class Lexer
       OPERATORS = {
         '+' => :plus,
@@ -39,7 +39,7 @@ module Sass
         end
 
         whitespace
-        constant || string || number || color || bool || op || ident ||
+        variable || string || number || color || bool || op || ident ||
           (raise SyntaxError.new("Syntax error in '#{@scanner.string}' at '#{@scanner.rest}'."))
       end
 
@@ -62,7 +62,7 @@ module Sass
         @scanner.scan(/\s*/)
       end
 
-      def constant
+      def variable
         return unless @scanner.scan(/!(\w+)/)
         [:const, @scanner[1]]
       end
@@ -74,14 +74,14 @@ module Sass
 
       def string
         return unless @scanner.scan(/"((?:\\.|[^"\\])*)"/)
-        [:string, Constant::String.new(@scanner[1].gsub(/\\(.)/, '\1'))]
+        [:string, Script::String.new(@scanner[1].gsub(/\\(.)/, '\1'))]
       end
 
       def number
         return unless @scanner.scan(/(-)?(?:(\d*\.\d+)|(\d+))([a-zA-Z%]+)?/)
         value = @scanner[2] ? @scanner[2].to_f : @scanner[3].to_i
         value = -value if @scanner[1]
-        [:number, Constant::Number.new(value, Array(@scanner[4]))]
+        [:number, Script::Number.new(value, Array(@scanner[4]))]
       end
 
       COLOR = /\##{"([0-9a-fA-F]{1,2})" * 3}|(#{Color::HTML4_COLORS.keys.join("|")})/
@@ -93,12 +93,12 @@ module Sass
                 else
                   (1..3).map {|i| @scanner[i]}.map {|num| num.ljust(2, num).to_i(16)}
                 end
-        [:color, Constant::Color.new(value)]
+        [:color, Script::Color.new(value)]
       end
 
       def bool
         return unless s = @scanner.scan(/(true|false)\b/)
-        [:bool, Constant::Bool.new(s == 'true')]
+        [:bool, Script::Bool.new(s == 'true')]
       end
 
       def op
diff --git a/lib/sass/script/literal.rb b/lib/sass/script/literal.rb
new file mode 100644
index 00000000..fbe935a4
--- /dev/null
+++ b/lib/sass/script/literal.rb
@@ -0,0 +1,56 @@
+class Sass::Script::Literal # :nodoc:
+  require 'sass/script/string'
+  require 'sass/script/number'
+  require 'sass/script/color'
+  require 'sass/script/bool'
+
+  attr_reader :value
+
+  def initialize(value = nil)
+    @value = value
+  end
+
+  def perform
+    self
+  end
+
+  def and(other)
+    to_bool ? other : self
+  end
+
+  def or(other)
+    to_bool ? self : other
+  end
+
+  def eq(other)
+    Sass::Script::Bool.new(self.class == other.class && self.value == other.value)
+  end
+
+  def neq(other)
+    Sass::Script::Bool.new(!eq(other).to_bool)
+  end
+
+  def unary_not
+    Sass::Script::Bool.new(!to_bool)
+  end
+
+  def concat(other)
+    Sass::Script::String.new("#{self.to_s} #{other.to_s}")
+  end
+
+  def comma(other)
+    Sass::Script::String.new("#{self.to_s}, #{other.to_s}")
+  end
+
+  def inspect
+    value.inspect
+  end
+
+  def to_bool
+    true
+  end
+
+  def to_i
+    raise SyntaxError.new("#{value.dump} is not an integer.")
+  end
+end
diff --git a/lib/sass/constant/number.rb b/lib/sass/script/number.rb
similarity index 97%
rename from lib/sass/constant/number.rb
rename to lib/sass/script/number.rb
index ae87698b..d1a01f03 100644
--- a/lib/sass/constant/number.rb
+++ b/lib/sass/script/number.rb
@@ -1,6 +1,6 @@
-require 'sass/constant/literal'
+require 'sass/script/literal'
 
-module Sass::Constant
+module Sass::Script
   class Number < Literal # :nodoc:
 
     attr_reader :numerator_units, :denominator_units
@@ -20,7 +20,7 @@ module Sass::Constant
       elsif other.is_a?(Color)
         other.plus(self)
       else
-        Sass::Constant::String.new(self.to_s + other.to_s)
+        Sass::Script::String.new(self.to_s + other.to_s)
       end
     end
 
@@ -66,7 +66,7 @@ module Sass::Constant
     end
 
     def eq(other)
-      Sass::Constant::Bool.new(super.to_bool &&
+      Sass::Script::Bool.new(super.to_bool &&
         self.numerator_units.sort == other.numerator_units.sort &&
         self.denominator_units.sort == other.denominator_units.sort)
     end
diff --git a/lib/sass/constant/operation.rb b/lib/sass/script/operation.rb
similarity index 78%
rename from lib/sass/constant/operation.rb
rename to lib/sass/script/operation.rb
index bd0c473e..75cbe820 100644
--- a/lib/sass/constant/operation.rb
+++ b/lib/sass/script/operation.rb
@@ -1,10 +1,10 @@
-require 'sass/constant/string'
-require 'sass/constant/number'
-require 'sass/constant/color'
-require 'sass/constant/functions'
-require 'sass/constant/unary_operation'
+require 'sass/script/string'
+require 'sass/script/number'
+require 'sass/script/color'
+require 'sass/script/functions'
+require 'sass/script/unary_operation'
 
-module Sass::Constant
+module Sass::Script
   class Operation # :nodoc:
     def initialize(operand1, operand2, operator)
       @operand1 = operand1
diff --git a/lib/sass/constant/parser.rb b/lib/sass/script/parser.rb
similarity index 87%
rename from lib/sass/constant/parser.rb
rename to lib/sass/script/parser.rb
index 66df6247..ee829b21 100644
--- a/lib/sass/constant/parser.rb
+++ b/lib/sass/script/parser.rb
@@ -1,11 +1,11 @@
-require 'sass/constant/lexer'
+require 'sass/script/lexer'
 
 module Sass
-  module Constant
+  module Script
     class Parser
-      def initialize(str, constants = {})
+      def initialize(str, environment = {})
         @lexer = Lexer.new(str)
-        @constants = constants
+        @environment = environment
       end
 
       def parse
@@ -67,10 +67,10 @@ RUBY
       def funcall
         return paren unless name = try_tok(:ident)
         # An identifier without arguments is just a string
-        return Constant::String.new(name.last) unless try_tok(:lparen)
+        return Script::String.new(name.last) unless try_tok(:lparen)
         args = arglist || []
         assert_tok(:rparen)
-        Constant::Funcall.new(name.last, args)
+        Script::Funcall.new(name.last, args)
       end
 
       def arglist
@@ -80,17 +80,17 @@ RUBY
       end
 
       def paren
-        return constant unless try_tok(:lparen)
+        return variable unless try_tok(:lparen)
         e = assert_expr(:expr)
         assert_tok(:rparen)
         return e
       end
 
-      def constant
+      def variable
         return literal unless c = try_tok(:const)
-        (val = @constants[c.last]) && (return val)
+        (val = @environment[c.last]) && (return val)
 
-        raise SyntaxError.new("Undefined constant: \"!#{c.last}\".")
+        raise SyntaxError.new("Undefined variable: \"!#{c.last}\".")
       end
 
       def literal
diff --git a/lib/sass/script/string.rb b/lib/sass/script/string.rb
new file mode 100644
index 00000000..9d643afa
--- /dev/null
+++ b/lib/sass/script/string.rb
@@ -0,0 +1,33 @@
+require 'sass/script/literal'
+
+module Sass::Script
+  class String < Literal # :nodoc:
+    def plus(other)
+      Sass::Script::String.new(self.to_s + other.to_s)
+    end
+
+    def minus(other)
+      Sass::Script::String.new("#{self.to_s}-#{other.to_s}")
+    end
+
+    def unary_minus
+      Sass::Script::String.new("-#{self.to_s}")
+    end
+
+    def div(other)
+      Sass::Script::String.new("#{self.to_s}/#{other.to_s}")
+    end
+
+    def unary_div
+      Sass::Script::String.new("/#{self.to_s}")
+    end
+
+    def funcall(other)
+      Sass::Script::String.new("#{self.to_s}(#{other.to_s})")
+    end
+
+    def to_s
+      @value
+    end
+  end
+end
diff --git a/lib/sass/constant/unary_operation.rb b/lib/sass/script/unary_operation.rb
similarity index 96%
rename from lib/sass/constant/unary_operation.rb
rename to lib/sass/script/unary_operation.rb
index ddb6df9f..7209515e 100644
--- a/lib/sass/constant/unary_operation.rb
+++ b/lib/sass/script/unary_operation.rb
@@ -1,4 +1,4 @@
-module Sass::Constant
+module Sass::Script
   class UnaryOperation # :nodoc:
     def initialize(operand, operator)
       @operand = operand
diff --git a/test/sass/engine_test.rb b/test/sass/engine_test.rb
index f11bab6d..00e69993 100755
--- a/test/sass/engine_test.rb
+++ b/test/sass/engine_test.rb
@@ -31,11 +31,11 @@ class SassEngineTest < Test::Unit::TestCase
     "a\n  b : c" => 'Invalid attribute: "b : c".',
     "a\n  b=c: d" => 'Invalid attribute: "b=c: d".',
     ":a" => 'Attributes aren\'t allowed at the root of a document.',
-    "!" => 'Invalid constant: "!".',
-    "!a" => 'Invalid constant: "!a".',
-    "! a" => 'Invalid constant: "! a".',
-    "!a b" => 'Invalid constant: "!a b".',
-    "a\n  :b c\n  !d = 3" => "Constants may only be declared at the root of a document.",
+    "!" => 'Invalid variable: "!".',
+    "!a" => 'Invalid variable: "!a".',
+    "! a" => 'Invalid variable: "! a".',
+    "!a b" => 'Invalid variable: "!a b".',
+    "a\n  :b c\n  !d = 3" => "Variables may only be declared at the root of a document.",
     "!a = 1b + 2c" => "Incompatible units: 'c' and 'b'.",
     "a\n  :b= 1b * 2c" => "2b*c isn't a valid CSS value.",
     "a\n  :b= 1b % 2c" => "Cannot modulo by a number with units: 2c.",
@@ -46,7 +46,7 @@ class SassEngineTest < Test::Unit::TestCase
     "a,\n  :b c" => ["Rules can\'t end in commas.", 1],
     "a," => "Rules can\'t end in commas.",
     "a,\n!b = c" => ["Rules can\'t end in commas.", 1],
-    "!a = b\n  :c d\n" => "Illegal nesting: Nothing may be nested beneath constants.",
+    "!a = b\n  :c d\n" => "Illegal nesting: Nothing may be nested beneath variable declarations.",
     "@import foo.sass" => "File to import not found or unreadable: foo.sass.",
     "@import templates/basic\n  foo" => "Illegal nesting: Nothing may be nested beneath import directives.",
     "foo\n  @import templates/basic" => "Import directives may only be used at the root of a document.",
@@ -68,7 +68,7 @@ class SassEngineTest < Test::Unit::TestCase
     "=a(b)" => 'Mixin argument "b" must begin with an exclamation point (!).',
     "=a(,)" => "Mixin arguments can't be empty.",
     "=a(!)" => "Mixin arguments can't be empty.",
-    "=a(!foo bar)" => "Invalid constant \"!foo bar\".",
+    "=a(!foo bar)" => "Invalid variable \"!foo bar\".",
     "=foo\n  bar: baz\n+foo" => ["Attributes aren't allowed at the root of a document.", 2],
     "a-\#{!b\n  c: d" => ["Unbalanced brackets.", 1],
     "=a(!b = 1, !c)" => "Required arguments must not follow optional arguments \"!c\".",
diff --git a/test/sass/functions_test.rb b/test/sass/functions_test.rb
index 6183e70c..ab43de96 100644
--- a/test/sass/functions_test.rb
+++ b/test/sass/functions_test.rb
@@ -1,6 +1,6 @@
 require 'test/unit'
 require File.dirname(__FILE__) + '/../../lib/sass'
-require 'sass/constant'
+require 'sass/script'
 
 class SassFunctionTest < Test::Unit::TestCase
   def test_hsl
@@ -46,6 +46,6 @@ class SassFunctionTest < Test::Unit::TestCase
   private
 
   def assert_rgb_hsl(rgb, hsl)
-    assert_equal(rgb, Sass::Constant::Functions.hsl(*hsl.map(&Sass::Constant::Parser.method(:parse))).value)
+    assert_equal(rgb, Sass::Script::Functions.hsl(*hsl.map(&Sass::Script::Parser.method(:parse))).value)
   end
 end
diff --git a/test/sass/plugin_test.rb b/test/sass/plugin_test.rb
index b4323f3c..b0711f00 100644
--- a/test/sass/plugin_test.rb
+++ b/test/sass/plugin_test.rb
@@ -5,7 +5,7 @@ require 'fileutils'
 
 class SassPluginTest < Test::Unit::TestCase
   @@templates = %w{
-    complex constants parent_ref import alt
+    complex script parent_ref import alt
     subdir/subdir subdir/nested_subdir/nested_subdir
   }
 
@@ -52,7 +52,7 @@ class SassPluginTest < Test::Unit::TestCase
     File.delete(tempfile_loc('bork'))
     Sass::Plugin.update_stylesheets
     File.open(tempfile_loc('bork')) do |file|
-      assert_equal("/*\nSass::SyntaxError: Undefined constant: \"!bork\".\non line 2 of #{template_loc('bork')}\n\n1: bork\n2:   :bork= !bork", file.read.split("\n")[0...6].join("\n"))
+      assert_equal("/*\nSass::SyntaxError: Undefined variable: \"!bork\".\non line 2 of #{template_loc('bork')}\n\n1: bork\n2:   :bork= !bork", file.read.split("\n")[0...6].join("\n"))
     end
     File.delete(tempfile_loc('bork'))
   end
diff --git a/test/sass/results/constants.css b/test/sass/results/script.css
similarity index 100%
rename from test/sass/results/constants.css
rename to test/sass/results/script.css
diff --git a/test/sass/templates/constants.sass b/test/sass/templates/script.sass
similarity index 100%
rename from test/sass/templates/constants.sass
rename to test/sass/templates/script.sass