An application program may go through a sequence of versions. A particular version, compiled for a particular platform, is called an application version. An application version can consist of multiple files: for example, a controller script, pre- and post-processing programs, and a primary executable.

Each application version has an integer version number. Projects can assign version numbers however they like; for example, version 304 might represent major version 3 and minor version 4. Version numbers should be used consistently across platforms; Windows version 304 should be computationally identical to Mac version 304.

Each application has a minimum version. When a client is sent work for an application, it is also sent the latest application version for its platform. It is sent work only if this version is the minimum or greater.

Application versions are maintained in the app_version table in the BOINC DB. Each entry includes an XML document describing the files that make up the application version:

<file_info> ... 
</file_info>
[ ... 
]
<app_version>
    <app_name>foobar</app_name>
    <version_num>4</version_num>
    <file_ref>
        <file_name>program_1</file_name>
        <main_program/>
    </file_ref>
    <file_ref>
        <file_name>library_12</file_name>
    </file_ref>
</app_version>