ASP.NET Application Folders : Directory Structure « ASP.Net Instroduction « ASP.NET Tutorial

\App_Code Folder stores your classes, .wsdl files, and typed datasets. 
Items in this folder are automatically available to all the pages within your solution. 

Because all the classes contained in this folder are built into a single assembly, 
you cannot have classes of different languages sitting in the root \App_Code folder 


In order to work with multiple languages in your \App_Code folder, 
you must make some changes to the folder structure and to the web.config file.

The first step is to add two new subfolders to the \App_Code folder - a \VB folder and a \CS folder. 


Structuring the web.config file
      <add directoryName="VB"></add>
      <add directoryName="CS"></add>

1.2.Directory Structure
1.2.1.Application Directory Structure
1.2.2.ASP.NET Application Folders
1.2.3.ASP.NET Page Directives
1.2.4.directives in ASP.NET
1.2.5.@Page directive
1.2.6.Page Directives, code section and layout