This article surveys the evolution of the international arms market since the end of the Cold War. It begins with the policy context, the choices made by the national Ministries of Defence and the constraints they faced. It then looks at the choices available to the arms producers: convert, diversify, divest, co-operate or concentrate. These choices, by governments and firms, produced a large increase in the degree of concentration. The share of the five largest firms increased from just over 20% in 1990 to 45% in 1998, and it has increased further since then. Finally, the author looks at the economic adjustment in response to these shocks.