Knowledge of the query string helps in debugging a problem if values from the query string are used. You could extend the code in Application_Error and add other useful information such as cookies and form collections. For more information about accessing these kinds of collections, pick up a copy of Professional ASP.NET 4.5 published by Wrox. Alternatively, look into ELMAH—the Error Logging Modules and Handlers project—at http://code.google.com/p/elmah/, which is an open source project run by Atif Aziz that is aimed at catching and logging exceptions. The beauty of the ELMAH project is that it’s extremely simple to integrate in your site (no programming required, you just need to add a few lines of configuration code to your Web.config file). And even better: there’s a NuGet package available that adds the necessary files and configuration for you. Simply run the following command from the Package Manager Console: