diff --git a/lib/oga/xpath/evaluator.rb b/lib/oga/xpath/evaluator.rb
index 9194ce5..35300d0 100644
--- a/lib/oga/xpath/evaluator.rb
+++ b/lib/oga/xpath/evaluator.rb
@@ -1185,6 +1185,21 @@ module Oga
         return sum
       end
 
+      ##
+      # Processes the `floor()` function call.
+      #
+      # This function floors a numeric value and returns the result as a float.
+      #
+      # @param [Oga::XML::NodeSet] context
+      # @param [Oga::XPath::Node] expression
+      # @return [Float]
+      #
+      def on_call_floor(context, expression)
+        number = on_call_number(context, expression)
+
+        return number.nan? ? number : number.floor.to_f
+      end
+
       ##
       # Processes an `(int)` node.
       #
diff --git a/spec/oga/xpath/evaluator/calls/floor_spec.rb b/spec/oga/xpath/evaluator/calls/floor_spec.rb
new file mode 100644
index 0000000..a8208f0
--- /dev/null
+++ b/spec/oga/xpath/evaluator/calls/floor_spec.rb
@@ -0,0 +1,30 @@
+require 'spec_helper'
+
+describe Oga::XPath::Evaluator do
+  context 'floor() function' do
+    before do
+      @document  = parse('<root>10.123</root>')
+      @evaluator = described_class.new(@document)
+    end
+
+    example 'return the floor of a literal number' do
+      @evaluator.evaluate('floor(10.123)').should == 10.0
+    end
+
+    example 'return the floor of a literal string' do
+      @evaluator.evaluate('floor("10.123")').should == 10.0
+    end
+
+    example 'return the floor of a node set' do
+      @evaluator.evaluate('floor(root)').should == 10.0
+    end
+
+    example 'return NaN for empty node sets' do
+      @evaluator.evaluate('floor(foo)').should be_nan
+    end
+
+    example 'return NaN for an empty literal string' do
+      @evaluator.evaluate('floor("")').should be_nan
+    end
+  end
+end