diff --git a/lib/oga/xml/querying.rb b/lib/oga/xml/querying.rb
index 1eee81c..80691b0 100644
--- a/lib/oga/xml/querying.rb
+++ b/lib/oga/xml/querying.rb
@@ -10,6 +10,7 @@ module Oga
       #     document = Oga.parse_xml <<-EOF
       #     <people>
       #       <person age="25">Alice</person>
+      #       <ns:person xmlns:ns="http://example.net">Bob</ns:person>
       #     </people>
       #     EOF
       #
@@ -25,15 +26,23 @@ module Oga
       #
       #     document.xpath('people/person[@age = $age]', 'age' => 25)
       #
+      # Using namespace aliases:
+      #
+      #     namespaces = {'example' => 'http://example.net'}
+      #     document.xpath('people/example:person', namespaces: namespaces)
+      #
       # @param [String] expression The XPath expression to run.
       #
       # @param [Hash] variables Variables to bind. The keys of this Hash should
       #  be String values.
       #
+      # @param [Hash] namespaces Namespace aliases. The keys of this Hash should
+      #  be String values.
+      #
       # @return [Oga::XML::NodeSet]
-      def xpath(expression, variables = {})
+      def xpath(expression, variables = {}, namespaces: nil)
         ast   = XPath::Parser.parse_with_cache(expression)
-        block = XPath::Compiler.compile_with_cache(ast)
+        block = XPath::Compiler.compile_with_cache(ast, namespaces: namespaces)
 
         block.call(self, variables)
       end
diff --git a/lib/oga/xpath/compiler.rb b/lib/oga/xpath/compiler.rb
index ec711b3..d407fdf 100644
--- a/lib/oga/xpath/compiler.rb
+++ b/lib/oga/xpath/compiler.rb
@@ -42,12 +42,16 @@ module Oga
       # Compiles and caches an AST.
       #
       # @see [#compile]
-      def self.compile_with_cache(ast)
-        CACHE.get_or_set(ast) { new.compile(ast) }
+      def self.compile_with_cache(ast, namespaces: nil)
+        cache_key = namespaces ? [ast, namespaces] : ast
+        CACHE.get_or_set(cache_key) { new(namespaces: namespaces).compile(ast) }
       end
 
-      def initialize
+      # @param [Hash] namespaces
+      def initialize(namespaces: nil)
         reset
+
+        @namespaces = namespaces
       end
 
       # Resets the internal state.
@@ -1385,7 +1389,18 @@ module Oga
         end
 
         if ns and ns != STAR
-          ns_match  = input.namespace_name.eq(string(ns))
+          if @namespaces
+            ns_uri = @namespaces[ns]
+            ns_match = 
+              if ns_uri
+                input.namespace.and(input.namespace.uri.eq(string(ns_uri)))
+              else
+                self.false
+              end
+          else
+            ns_match = input.namespace_name.eq(string(ns))
+          end
+
           condition = condition ? condition.and(ns_match) : ns_match
         end
 
diff --git a/spec/oga/xml/querying_spec.rb b/spec/oga/xml/querying_spec.rb
index e0400e1..df20813 100644
--- a/spec/oga/xml/querying_spec.rb
+++ b/spec/oga/xml/querying_spec.rb
@@ -3,6 +3,10 @@ require 'spec_helper'
 describe Oga::XML::Querying do
   before do
     @document = parse('<a>foo</a>')
+    @document2 = parse('<a xmlns:x="y"><x:b>bar</x:b></a>')
+    @namespaces = {
+      "n" => "y"
+    }
   end
 
   describe '#xpath' do
@@ -17,6 +21,10 @@ describe Oga::XML::Querying do
     it 'evaluates an expression using a variable' do
       expect(@document.xpath('$number', 'number' => 10)).to eq(10)
     end
+
+    it 'respects custom namespace aliases' do
+      expect(@document2.xpath('a/n:b', namespaces: @namespaces)[0].text).to eq('bar')
+    end
   end
 
   describe '#at_xpath' do
@@ -31,6 +39,10 @@ describe Oga::XML::Querying do
     it 'evaluates an expression using a variable' do
       expect(@document.at_xpath('$number', 'number' => 10)).to eq(10)
     end
+
+    it 'respects custom namespace aliases' do
+      expect(@document2.at_xpath('a/n:b', namespaces: @namespaces).text).to eq('bar')
+    end
   end
 
   describe '#css' do
diff --git a/spec/oga/xpath/compiler/namespace_aliases_spec.rb b/spec/oga/xpath/compiler/namespace_aliases_spec.rb
new file mode 100644
index 0000000..98726b7
--- /dev/null
+++ b/spec/oga/xpath/compiler/namespace_aliases_spec.rb
@@ -0,0 +1,40 @@
+require 'spec_helper'
+
+describe Oga::XPath::Compiler do
+  before do
+    @document = parse('<root xmlns:x="y"><x:a></x:a><b x:num="10"></b></root>')
+    @root = @document.children[0]
+    @a = @root.children[0]
+    @b = @root.children[1]
+    @attr = @b.attributes[0]
+    @namespaces = {
+      "n" => "y"
+    }
+  end
+
+  describe 'with custom namespace aliases' do
+    it 'uses aliases when querying an element' do
+      expect(evaluate_xpath(@document, 'root/n:a', namespaces: @namespaces)).to eq(node_set(@a))
+    end
+
+    it "doesn't use namespaces in XPath expression when querying an element" do
+      expect(evaluate_xpath(@document, 'root/x:a', namespaces: @namespaces)).to eq(node_set)
+    end
+
+    it 'uses aliases when querying an attribute' do
+      expect(evaluate_xpath(@document, 'root/b/@n:num', namespaces: @namespaces)).to eq(node_set(@attr))
+    end
+
+    it "doesn't use namespaces in XPath expression when querying an attribute" do
+      expect(evaluate_xpath(@document, 'root/b/@x:num', namespaces: @namespaces)).to eq(node_set)
+    end
+
+    it 'uses aliases when querying an element with a namespaced attribute' do
+      expect(evaluate_xpath(@document, 'root/b[@n:num]', namespaces: @namespaces)).to eq(node_set(@b))
+    end
+
+    it "doesn't use namespaces in XPath expression when querying an element with a namespaced attribute" do
+      expect(evaluate_xpath(@document, 'root/b[@x:num]', namespaces: @namespaces)).to eq(node_set)
+    end
+  end
+end
diff --git a/spec/support/evaluation_helpers.rb b/spec/support/evaluation_helpers.rb
index 5bcbb55..f006d8f 100644
--- a/spec/support/evaluation_helpers.rb
+++ b/spec/support/evaluation_helpers.rb
@@ -5,9 +5,9 @@ module Oga
     # @param [String] xpath
     # @return [Oga::XML::NodeSet]
     #
-    def evaluate_xpath(document, xpath = self.class.description)
+    def evaluate_xpath(document, xpath = self.class.description, namespaces: nil)
       ast      = parse_xpath(xpath)
-      compiler = Oga::XPath::Compiler.new
+      compiler = Oga::XPath::Compiler.new(namespaces: namespaces)
       block    = compiler.compile(ast)
 
       block.call(document)