diff --git a/lib/oga/xpath/compiler.rb b/lib/oga/xpath/compiler.rb
index 507381a..e5565a1 100644
--- a/lib/oga/xpath/compiler.rb
+++ b/lib/oga/xpath/compiler.rb
@@ -1,7 +1,7 @@
 module Oga
   module XPath
     ##
-    # Compiling of XPath ASTs into Ruby source code.
+    # Compiling of XPath ASTs into Ruby code.
     #
     # The Compiler class can be used to turn an XPath AST into Ruby source code
     # that can be executed to match XML nodes in a given input document/element.
@@ -9,6 +9,15 @@ module Oga
     # recompiling the same expression over and over again.
     #
     class Compiler
+      ##
+      # Compiles an XPath AST into a Ruby Proc.
+      #
+      # @param [AST::Node] ast
+      # @return [Proc]
+      #
+      def compile(ast)
+
+      end
     end # Compiler
   end # XPath
 end # Oga
diff --git a/spec/oga/xpath/compiler_spec.rb b/spec/oga/xpath/compiler_spec.rb
new file mode 100644
index 0000000..61e6218
--- /dev/null
+++ b/spec/oga/xpath/compiler_spec.rb
@@ -0,0 +1,38 @@
+require 'spec_helper'
+
+describe Oga::XPath::Compiler do
+  before do
+    @compiler = described_class.new
+  end
+
+  describe '#compile' do
+    it 'returns a Proc as a lambda' do
+      ast   = parse_xpath('foo')
+      block = @compiler.compile(ast)
+
+      block.should be_an_instance_of(Proc)
+      block.lambda?.should == true
+    end
+
+    it 'returns a Proc with a single required argument' do
+      ast = parse_xpath('foo')
+
+      # Only the input document is required.
+      @compiler.compile(ast).arity.should == 1
+    end
+
+    xit 'caches a compiled Proc for a given XPath AST' do
+      # TODO
+    end
+
+    describe 'calling the compiled Proc' do
+      it 'returns a NodeSet' do
+        doc   = parse_xml('<foo></foo>')
+        ast   = parse_xpath('foo')
+        block = @compiler.compile(ast)
+
+        block.call(doc).should be_an_instance_of(NodeSet)
+      end
+    end
+  end
+end