diff --git a/koans/about_to_str.rb b/koans/about_to_str.rb
new file mode 100644
index 0000000..964850d
--- /dev/null
+++ b/koans/about_to_str.rb
@@ -0,0 +1,54 @@
+require File.expand_path(File.dirname(__FILE__) + '/edgecase')
+
+class AboutToStr < EdgeCase::Koan
+
+  class CanNotBeTreatedAsString
+    def to_s
+      "non-string-like"
+    end
+  end
+
+  def test_to_s_returns_a_string_representation
+    not_like_a_string = CanNotBeTreatedAsString.new
+    assert_equal __, not_like_a_string.to_s
+  end
+
+  def test_normally_objects_cannot_be_used_where_strings_are_expected
+    assert_raise(___) do
+      File.exist?(CanNotBeTreatedAsString.new)
+    end
+  end
+
+  # ------------------------------------------------------------------
+
+  class CanBeTreatedAsString
+    def to_s
+      "string-like"
+    end
+
+    def to_str
+      to_s
+    end
+  end
+
+  def test_to_str_also_returns_a_string_representation
+    like_a_string = CanBeTreatedAsString.new
+    assert_equal __, like_a_string.to_str
+  end
+
+  def test_to_str_allows_objects_to_be_treated_as_strings
+    assert_equal __, File.exist?(CanBeTreatedAsString.new)
+  end
+
+  # ------------------------------------------------------------------
+
+  def acts_like_a_string?(string)
+    string = string.to_str if string.respond_to?(:to_str)
+    string.is_a?(String)
+  end
+
+  def test_user_defined_code_can_check_for_to_str
+    assert_equal __, acts_like_a_string?(CanNotBeTreatedAsString.new)
+    assert_equal __,  acts_like_a_string?(CanBeTreatedAsString.new)
+  end
+end
diff --git a/koans/path_to_enlightenment.rb b/koans/path_to_enlightenment.rb
index 641559a..64621bf 100644
--- a/koans/path_to_enlightenment.rb
+++ b/koans/path_to_enlightenment.rb
@@ -31,6 +31,7 @@ require 'about_scope'
 require 'about_class_methods'
 require 'about_message_passing'
 require 'about_proxy_object_project'
+require 'about_to_str'
 in_ruby_version("jruby") do
   require 'about_java_interop'
 end
diff --git a/src/about_to_str.rb b/src/about_to_str.rb
new file mode 100644
index 0000000..68c40b2
--- /dev/null
+++ b/src/about_to_str.rb
@@ -0,0 +1,54 @@
+require File.expand_path(File.dirname(__FILE__) + '/edgecase')
+
+class AboutToStr < EdgeCase::Koan
+
+  class CanNotBeTreatedAsString
+    def to_s
+      "non-string-like"
+    end
+  end
+
+  def test_to_s_returns_a_string_representation
+    not_like_a_string = CanNotBeTreatedAsString.new
+    assert_equal __("non-string-like"), not_like_a_string.to_s
+  end
+
+  def test_normally_objects_cannot_be_used_where_strings_are_expected
+    assert_raise(___(TypeError)) do
+      File.exist?(CanNotBeTreatedAsString.new)
+    end
+  end
+
+  # ------------------------------------------------------------------
+
+  class CanBeTreatedAsString
+    def to_s
+      "string-like"
+    end
+
+    def to_str
+      to_s
+    end
+  end
+
+  def test_to_str_also_returns_a_string_representation
+    like_a_string = CanBeTreatedAsString.new
+    assert_equal __("string-like"), like_a_string.to_str
+  end
+
+  def test_to_str_allows_objects_to_be_treated_as_strings
+    assert_equal __(false), File.exist?(CanBeTreatedAsString.new)
+  end
+
+  # ------------------------------------------------------------------
+
+  def acts_like_a_string?(string)
+    string = string.to_str if string.respond_to?(:to_str)
+    string.is_a?(String)
+  end
+
+  def test_user_defined_code_can_check_for_to_str
+    assert_equal __(false), acts_like_a_string?(CanNotBeTreatedAsString.new)
+    assert_equal __(true),  acts_like_a_string?(CanBeTreatedAsString.new)
+  end
+end
diff --git a/src/path_to_enlightenment.rb b/src/path_to_enlightenment.rb
index 641559a..64621bf 100644
--- a/src/path_to_enlightenment.rb
+++ b/src/path_to_enlightenment.rb
@@ -31,6 +31,7 @@ require 'about_scope'
 require 'about_class_methods'
 require 'about_message_passing'
 require 'about_proxy_object_project'
+require 'about_to_str'
 in_ruby_version("jruby") do
   require 'about_java_interop'
 end