diff --git a/lib/oga/xpath/evaluator.rb b/lib/oga/xpath/evaluator.rb
index 03c6ba2..1ca2d28 100644
--- a/lib/oga/xpath/evaluator.rb
+++ b/lib/oga/xpath/evaluator.rb
@@ -982,6 +982,26 @@ module Oga
         return on_call_string(context, expression).length.to_f
       end
 
+      ##
+      # Processes the `normalize-space()` function call.
+      #
+      # This function strips the 1st argument string *or* the current context
+      # node of leading/trailing whitespace as well as replacing multiple
+      # whitespace sequences with single spaces.
+      #
+      # @example
+      #  normalize-space(" fo  o    ") # => "fo o"
+      #
+      # @param [Oga::XML::NodeSet] context
+      # @param [Oga::XPath::Node] expression
+      # @return [String]
+      #
+      def on_call_normalize_space(context, expression = nil)
+        str = on_call_string(context, expression)
+
+        return str.strip.gsub(/\s+/, ' ')
+      end
+
       ##
       # Processes an `(int)` node.
       #
diff --git a/spec/oga/xpath/evaluator/calls/normalize_space_spec.rb b/spec/oga/xpath/evaluator/calls/normalize_space_spec.rb
new file mode 100644
index 0000000..9337a8a
--- /dev/null
+++ b/spec/oga/xpath/evaluator/calls/normalize_space_spec.rb
@@ -0,0 +1,40 @@
+require 'spec_helper'
+
+describe Oga::XPath::Evaluator do
+  context 'normalize-space() function' do
+    before do
+      @document  = parse('<root><a> fo   o </a></root>')
+      @evaluator = described_class.new(@document)
+    end
+
+    context 'outside predicates' do
+      example 'normalize a literal string' do
+        @evaluator.evaluate('normalize-space(" fo  o ")').should == 'fo o'
+      end
+
+      example 'normalize a string in a node set' do
+        @evaluator.evaluate('normalize-space(root/a)').should == 'fo o'
+      end
+
+      example 'normalize an integer' do
+        @evaluator.evaluate('normalize-space(10)').should == '10'
+      end
+
+      example 'normalize a float' do
+        @evaluator.evaluate('normalize-space(10.5)').should == '10.5'
+      end
+    end
+
+    context 'inside predicates' do
+      before do
+        @set = @evaluator.evaluate('root/a[normalize-space()]')
+      end
+
+      it_behaves_like :node_set, :length => 1
+
+      example 'return the <a> node' do
+        @set[0].should == @document.children[0].children[0]
+      end
+    end
+  end
+end