The global.asa file is an optional file that stores script procedures and objects used globally by an application. There can only be one global.asa file per ASP application. The file must be named global.asa, and must be stored in the root directory of the application (the top-level directory containing all application files and sub-directories).

The only script procedures you can declare in the global.asa file are listed below :

• Application_OnStart event
• Application_OnEnd event
• Session_OnStart event
• Session_OnEnd event

Scripts that do not have session or application scope cause the server to return an error. Global.asa files that do not specify Application and Session events are ignored.

Script procedures declared in the global.asa file cannot be called from ASP pages in an application.

Leeched from : http://docs.sun.com/source/817-2514-10/Ch8_BuildApp14.html