N-tier (multi-tier) applications have become the norm for building enterprise software today. To most people, an N-tier application is anything that is divided into discrete logical parts. The most common choice is a three-part breakdown: presentation, business logic, and data (although other possibilities exist). N-tier applications first emerged as a way of solving some of the problems associated with traditional client/server applications, but with the arrival of the Web, this architecture has come to dominate new development.
