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Client/server computing defines an architecture in which program logic is distributed between client systems and server systems. Client/server computing is a result of trends in the 1980s to populate desktops with powerful computers that were connected via LANs to back-end database servers or application servers. It was a model designed to replace the mainframe computing model in which all the processing was done by a centralized system.

With the rise of the Internet, the client/server computing model has evolved from a two-way relationship (usually called a two-tiered model) to a three-tiered or multitiered model in which clients communicate with intermediate application servers or Web servers, which in turn communicate with back-end data servers and/or legacy systems. The intermediate servers then return the results of database queries back to clients. See "Multitiered Architectures" for a description and illustration.