diff --git a/Library/Homebrew/dependencies.rb b/Library/Homebrew/dependencies.rb
index 16d2768f25..3526888399 100644
--- a/Library/Homebrew/dependencies.rb
+++ b/Library/Homebrew/dependencies.rb
@@ -61,17 +61,17 @@ private
     case spec
     when :autoconf, :automake, :bsdmake, :libtool
       # Xcode no longer provides autotools or some other build tools
-      Dependency.new(spec.to_s) unless MacOS::Xcode.provides_autotools?
+      Dependency.new(spec.to_s, tag) unless MacOS::Xcode.provides_autotools?
     when :libpng, :freetype, :pixman, :fontconfig, :cairo
       if MacOS.version >= :mountain_lion
-        Dependency.new(spec.to_s)
+        Dependency.new(spec.to_s, tag)
       else
         X11Dependency.new(tag)
       end
     when :x11
       X11Dependency.new(tag)
     when :xcode
-      XCodeDependency.new
+      XcodeDependency.new(tag)
     else
       raise "Unsupported special dependency #{spec}"
     end
@@ -82,47 +82,76 @@ end
 
 # A list of formula dependencies.
 class Dependencies < Array
-  def include? dependency_name
-    self.any?{|d| d.name == dependency_name}
+  def <<(o)
+    super(o) unless include? o
+  end
+end
+
+module Dependable
+  RESERVED_TAGS = [:build, :optional, :recommended]
+
+  def build?
+    tags.include? :build
+  end
+
+  def optional?
+    tags.include? :optional
+  end
+
+  def recommended?
+    tags.include? :recommended
+  end
+
+  def options
+    tags.reject { |tag| RESERVED_TAGS.include? tag }.map { |tag| '--'+tag.to_s }
   end
 end
 
 
 # A dependency on another Homebrew formula.
 class Dependency
+  include Dependable
+
   attr_reader :name, :tags
 
-  def initialize name, tags=nil
+  def initialize(name, *tags)
     @name = name
-    @tags = case tags
-      when Array then tags.each {|s| s.to_s}
-      when nil then []
-      else [tags.to_s]
-    end
+    @tags = [tags].flatten.compact
+  end
+
+  def hash
+    @name.hash
   end
 
   def to_s
     @name
   end
 
-  def ==(other_dep)
-    @name == other_dep.to_s
+  def ==(other)
+    @name == other.to_s
   end
 
-  def <=>(other_dep)
-    @name <=> other_dep.to_s
+  def <=>(other)
+    @name <=> other.to_s
   end
 
-  def options
-    @tags.select{|p|p.start_with? '--'}
+  def eql?(other)
+    other.is_a? self.class and hash == other.hash
   end
 end
 
-
 # A base class for non-formula requirements needed by formulae.
 # A "fatal" requirement is one that will fail the build if it is not present.
 # By default, Requirements are non-fatal.
 class Requirement
+  include Dependable
+
+  attr_reader :tags
+
+  def initialize(*tags)
+    @tags = tags.flatten.compact
+  end
+
   # Should return true if this requirement is met.
   def satisfied?; false; end
   # Should return true if not meeting this requirement should fail the build.
diff --git a/Library/Homebrew/requirements.rb b/Library/Homebrew/requirements.rb
index b7cc68a7c8..00c1612969 100644
--- a/Library/Homebrew/requirements.rb
+++ b/Library/Homebrew/requirements.rb
@@ -53,8 +53,10 @@ class X11Dependency < Requirement
   include Comparable
   attr_reader :min_version
 
-  def initialize min_version=nil
-    @min_version = min_version
+  def initialize(*tags)
+    tags.flatten!
+    @min_version = tags.shift if /(\d\.)+\d/ === tags.first
+    super
   end
 
   def fatal?; true; end
@@ -193,7 +195,7 @@ class ConflictRequirement < Requirement
   end
 end
 
-class XCodeDependency < Requirement
+class XcodeDependency < Requirement
   def fatal?; true; end
 
   def satisfied?
@@ -201,7 +203,7 @@ class XCodeDependency < Requirement
   end
 
   def message; <<-EOS.undent
-    A full installation of XCode.app is required to compile this software.
+    A full installation of Xcode.app is required to compile this software.
     Installing just the Command Line Tools is not sufficent.
     EOS
   end
diff --git a/Library/Homebrew/test/test_comparableset.rb b/Library/Homebrew/test/test_comparableset.rb
index d39ad51d6d..39f9b6f320 100644
--- a/Library/Homebrew/test/test_comparableset.rb
+++ b/Library/Homebrew/test/test_comparableset.rb
@@ -1,5 +1,6 @@
 require 'testing_env'
 require 'extend/set'
+require 'dependencies'
 
 class ComparableSetTests < Test::Unit::TestCase
   def setup
diff --git a/Library/Homebrew/test/test_dependencies.rb b/Library/Homebrew/test/test_dependencies.rb
new file mode 100644
index 0000000000..4758aad0a9
--- /dev/null
+++ b/Library/Homebrew/test/test_dependencies.rb
@@ -0,0 +1,36 @@
+require 'testing_env'
+require 'test/testball'
+require 'dependencies'
+
+class DependencyCollector
+  def find_dependency(name)
+    deps.find { |dep| dep.name == name }
+  end
+end
+
+class DependencyTests < Test::Unit::TestCase
+  def setup
+    @d = DependencyCollector.new
+  end
+
+  def test_dependency_creation
+    @d.add 'foo' => :build
+    @d.add 'bar' => ['--universal', :optional]
+    assert_not_nil @d.find_dependency('foo')
+    assert_equal 2, @d.find_dependency('bar').tags.length
+  end
+
+  def test_dependency_tags
+    assert Dependency.new('foo', :build).build?
+    assert Dependency.new('foo', [:build, :optional]).optional?
+    assert Dependency.new('foo', [:universal]).options.include? '--universal'
+    assert_empty Dependency.new('foo').tags
+  end
+
+  def test_no_duplicate_dependencies
+    @d.add 'foo'
+    @d.add 'foo' => :build
+    assert_equal 1, @d.deps.length
+    assert_empty @d.find_dependency('foo').tags
+  end
+end
diff --git a/Library/Homebrew/test/test_external_deps.rb b/Library/Homebrew/test/test_requirements.rb
similarity index 60%
rename from Library/Homebrew/test/test_external_deps.rb
rename to Library/Homebrew/test/test_requirements.rb
index b4ca0f6e6a..c8a8e1ba87 100644
--- a/Library/Homebrew/test/test_external_deps.rb
+++ b/Library/Homebrew/test/test_requirements.rb
@@ -1,8 +1,66 @@
 require 'testing_env'
-require 'extend/string'
 require 'test/testball'
-require 'formula_installer'
+require 'dependencies'
 
+class DependencyCollector
+  def find_requirement(klass)
+    requirements.find do |req|
+      klass === req
+    end
+  end
+end
+
+class RequirementTests < Test::Unit::TestCase
+  def setup
+    @d = DependencyCollector.new
+  end
+
+  def test_requirement_creation
+    @d.add :x11
+    assert_not_nil @d.find_requirement(X11Dependency)
+  end
+
+
+  def test_no_duplicate_requirements
+    2.times { @d.add :x11 }
+    assert_equal 1, @d.requirements.length
+  end
+end
+
+class RequirementTagTests < Test::Unit::TestCase
+  def setup
+    @d = DependencyCollector.new
+  end
+
+  def test_requirement_tags
+    @d.add :x11 => '2.5.1'
+    @d.add :xcode => :build
+    assert_empty @d.find_requirement(X11Dependency).tags
+    assert @d.find_requirement(XcodeDependency).build?
+  end
+
+  def test_x11_no_tag
+    @d.add :x11
+    assert_empty @d.find_requirement(X11Dependency).tags
+  end
+
+  def test_x11_min_version
+    @d.add :x11 => '2.5.1'
+    assert_equal '2.5.1', @d.find_requirement(X11Dependency).min_version
+  end
+
+  def test_x11_tag
+    @d.add :x11 => :optional
+    assert @d.find_requirement(X11Dependency).optional?
+  end
+
+  def test_x11_min_version_and_tag
+    @d.add :x11 => ['2.5.1', :optional]
+    dep = @d.find_requirement(X11Dependency)
+    assert_equal '2.5.1', dep.min_version
+    assert dep.optional?
+  end
+end
 
 class ExternalDepsTests < Test::Unit::TestCase
   def check_deps_fail specs