Some Myths People normally think if they have created UI (ASP.Net application project), BL (.Net Class Library Project), & DAL data access layer (.Net Class Library Project) and referencing these projects in their web project, they are following 3 tier architecture. I think creating a n tier application is more than this. What is tier? According to me tier means a stand-alone process which has some code to process. In the above scenario where ASP.Net Web Application is referencing BL and DAL, all the code is running in w3wp (server OS)/ aspnet_wp process which is known as worker process. So in real terms all this is single tier. Then question arises that, is it 1 tier application? If you are not dealing with databases or any other thing which has its own process then yes it is 1-tier architecture. Database makes it 2-tier architecture. As all the databases are run under some process. sqlservr is the process for SQL databases. Some people also say that a web application will always