Apache has mod_rewrite; now IIS has a small, cheap (free) rewriting module Ionic's ISAPI Rewriting Filter (IIRF). Specify rewrite rules using regular expressions. An incoming URL like http://foo/bar/bam can be translated into http://foo/baz/bam.jsp or http://foo/baz/bam.php. ASP.NET has a URL mapping mechanism, but it works only for filetypes that are handled by ASP.NET: aspx, ascx, asmx, and so on. For static files or non-ASP.NET files, (XML, GIF, JPEG, CSS), the ASP.NET mapping won't work cleanly. IIS, like Apache's HTTP server, has an extension mechanism: it is called the ISAPI filter. There are commercial ISAPI filters that endow IIS with the ability to re-write URLs. This is a cheap and powerful alternative. Version 2 includes enhancements for use on large-scale servers with many multiple Web sites, Now, install the ISAPI filter once, and configure each Web site or Web application independently.