An application server is a software engine that delivers applications to client computers or devices, typically through the Internet and using the HyperText Transfer Protocol. Application servers are distinguished from web servers by the extensive use of server-side dynamic content and frequent integration with database engines.

An application server handles most, if not all, of the business logic and data access of the application (a.k.a. centralization). The main benefit of an application server is the ease of application development, since applications need not be programmed; instead, they are assembled from building blocks provided by the application server. For example, a Wiki is an application server that allows users to build dynamic content assembled from articles. Moreover, Wikipedia is an assembled Wiki that delivers an encyclopedia stored in a filesystem, with changes to the encyclopedia stored in a database.

Application servers run on many platforms, and the term colloquially applies to two different software applications. The term is used to refer to servers of web-based applications, such as integrated platforms for e-commerce, content management systems, and web-site builders. Alternatively, the term is used as a synonym for web application framework.