Application Pages in SharePoint

Application pages allow you to create custom screens in SharePoint and make them available at any site level, similar to the accessdenied.aspx and error.aspx that come out of the box with SharePoint. To create an application page, follow the article by Ted Pattison to get the minimal code that is needed in an application page.

Once you have the page built you place it in the 12 hive in the Layouts folder. To access your cuastom page you then navigate to a site (i.e. http://sharepointserver/site/_layouts/nameofcustompage.aspx. This will display your custom page. You can access it at any level of your site.

Application pages provide an excellent way to add custom code to your site and can be debugged by attaching to the W3WP process on the SharePoint server that matches the AppId of the site you want.