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diff --git a/lib/Catalyst/Engine/CGI.pm b/lib/Catalyst/Engine/CGI.pm
index da95c6c..076f5b0 100644
--- a/lib/Catalyst/Engine/CGI.pm
+++ b/lib/Catalyst/Engine/CGI.pm
@@ -28,6 +28,43 @@ appropriate engine module.
 
 This is the Catalyst engine specialized for the CGI environment.
 
+=head1 PATH DECODING
+
+Most web server environments pass the requested path to the application using environment variables,
+from which Catalyst has to reconstruct the request base (i.e. the top level path to / in the application,
+exposed as C<< $c->request->base >>) and the request path below that base.
+
+There are two methods of doing this, both of which have advantages and disadvantages. Which method is used
+is determined by the C<< $c->config(use_request_uri_for_path) >> setting (which can either be true or false).
+
+=head2 use_request_uri_for_path => 0
+
+This is the default (and the) traditional method that Catalyst has used for determining the path information.
+The path is synthesised from a combination of the C<PATH_INFO> and C<SCRIPT_NAME> environment variables.
+The allows the application to behave correctly when C<mod_rewrite> is being used to redirect requests
+into the application, as these variables are adjusted by mod_rewrite to take account for the redirect.
+
+However this method has the major disadvantage that it is impossible to correctly decode some elements
+of the path, as RFC 3875 says: "C<< Unlike a URI path, the PATH_INFO is not URL-encoded, and cannot
+contain path-segment parameters. >>" This means PATH_INFO is B<always> decoded, and therefore Catalyst
+can't distinguish / vs %2F in paths (in addition to other encoded values).
+
+=head2 use_request_uri_for_path => 1
+
+This method uses the C<REQUEST_URI> and C<SCRIPT_NAME> environment variables. As C<REQUEST_URI> is never
+decoded, this means that applications using this mode can correctly handle URIs including the %2F character
+(i.e. with C<AllowEncodedSlashes> set to C<On> in Apache).
+
+Given that this method of path resolution is provably more correct, it is recommended that you use
+this unless you have a specific need to deploy your application in a non-standard environment, and you are
+aware of the implications of not being able to handle encoded URI paths correctly.
+
+However it also means that in a number of cases when the app isn't installed directly at a path, but instead
+is having paths rewritten into it (e.g. as a .cgi/fcgi in a public_html directory, with mod_rewrite in a
+.htaccess file, or when SSI is used to rewrite pages into the app, or when sub-paths of the app are exposed
+at other URIs than that which the app is 'normally' based at with C<mod_rewrite>), the resolution of
+C<< $c->request->base >> will be incorrect.
+
 =head1 OVERLOADED METHODS
 
 This class overloads some methods from C<Catalyst::Engine>.
@@ -117,6 +154,12 @@ sub prepare_path {
     my $scheme = $c->request->secure ? 'https' : 'http';
     my $host      = $ENV{HTTP_HOST}   || $ENV{SERVER_NAME};
     my $port      = $ENV{SERVER_PORT} || 80;
+
+    # fix up for IIS
+    if ($ENV{SERVER_SOFTWARE} && $ENV{SERVER_SOFTWARE} =~ m{IIS/[6-9]\.\d}) {
+        $ENV{PATH_INFO} =~ s/^\Q$ENV{SCRIPT_NAME}\E//;
+    }
+
     my $script_name = $ENV{SCRIPT_NAME};
     $script_name =~ s/([^$URI::uric])/$URI::Escape::escapes{$1}/go if $script_name;