an IIS server on a site level or a global level (i.e., they apply to all sites on an IIS server). Filters are initialised when the worker process is started and listens to all requests to the site on which it is installed. Common tasks performed by ISAPI filters include: Changing request data (URLs or headers) sent by the client Controlling which physical file gets mapped to the URL Controlling the user name and password used with anonymous or basic authentication Modifying or analyzing a request after authentication is complete Modifying a response going back to the client Running custom processing on "access denied" responses Running processing when a request is complete Run processing when a connection with the client is closed Performing special logging or traffic analysis. Performing custom authentication. Handling encryption and compression. Common ISAPI applications This is a list of common ISAPI applications implemented as ISAPI extensions: Active Server Pages (ASP), installed as standard ActiveVFP, Active Visual FoxPro installed on IIS ASP.NET, installed as standard on IIS 6.0 onwards ColdFusion, later versions of ColdFusion are installable on IIS Perl ISAPI (aka Perliis), available for free to install PHP, available for free to install, not maintained anymore. ISAPI development ISAPI applications can be developed using any development tool that can generate a Windows DLL. Wizards for generating ISAPI framework applications have been available in Microsoft development tools since Visual C++ 4.0. See also Internet Information Services ATL Server SAPI C++ PHP FastCGI References Microsoft application programming interfaces