A Firebird client is a program, usually written in a high-level language such as C, C++, Delphi, Java, PHP or Perl, that provides end-user access to the features and tools of the Firebird database management system and to data stored in databases. The isql interactive SQL utility is an example of a client application.

In the client/server model, applications never touch the database physically. Any application process converses with the server through the Firebird client library which resides on the client workstation. It surfaces a programming interface of function call structures known as the Firebird API. This client library must be installed on every user's workstation. Generally, other layers are also involved in the interface between the application program and the Firebird client, providing generic or application-language-specific mechanisms for populating and calling the API functions.

Firebird clients typically reside on remote workstations and connect to a Firebird server running on a host node in a network. Firebird also supports local connection, that is, a client application, the Firebird client library and the Firebird server all executing on the same physical box.

Firebird clients need not run on the same type of hardware and/or operating system as the server they connect to. It is quite common to have a number of Windows 98 or XP workstations talking to a server that runs under Windows NT, 2000 or 2003, or any of several flavours of UNIX or Linux.