OKB is a transliteration of the Russian initials of "опытно-конструкторское бюро" – opytno konstruktorskoye byuro, meaning 'experiment and design bureau'. During the Soviet era, OKBs were closed institutions working on design and prototyping of advanced technology, usually for military applications. The english language corresponding term for such bureau's occupation is Research and Development.
A bureau was officially identified by a number, and often semi-officially by the name of its lead designer – for example, OKB-51 was led by Pavel Sukhoi, and it eventually became known as the OKB of Sukhoi. Successful and famous bureaus often retained this name even after the death or replacement of their designers.
These relatively small, state-run organisations were not intended for the mass production of aircraft, rockets, or other vehicles or equipment which they designed. However, they usually had the facilities and resources to construct prototypes. Designs accepted by the state were then assigned to factories for mass production.
After the collapse of the Soviet Union, many OKBs became Scientific Production Organizations (Научно-производственное объединение) (NPO). There were some attempts to merge them in the 1990s, and there were widespread amalgamations in 2001–2006 to create "national champions", such as Almaz-Antey to consolidate SAM development.