Application

Application_start
Called when the first resource (such as a page) in an ASP.NET application is requested. The Application_Start method is called only one time during the life cycle of an application. You can use this method to perform startup tasks such as loading data into the cache and initializing static values.
You should set only static data during application start. Do not set any instance data because it will be available only to the first instance of the HttpApplication class that is created.

Application_Event
Raised at the appropriate time in the application life cycle, as listed in the application life cycle table earlier in this topic.
Application_Error can be raised at any phase in the application life cycle.
Application_EndRequest is the only event that is guaranteed to be raised in every request, because a request can be short-circuited. For example, if two modules handle the Application_BeginRequest event and the first one throws an exception, the Application_BeginRequest event will not be called for the second module. However, the Application_EndRequest method is always called to allow the application to clean up resources.


Application_End
Called once per lifetime of the application before the application is unloaded.