Petter St?lenheim and Eamon Surry

　　Transparency in the military sector has become an increasingly important international political issue since the 1980s. Levels of transparency in relation to military expenditure, arms production and arms trade still vary widely between countries, but the flow of information can generally be said to have improved in the past two decades. This is in part because of improved communications technologies that enable the easy publication and retrieval of information, but it is also due to a general acknowledgement that the disclosure of such information is in the public interest and does not usually jeopardize national security.

　　Put most simply, transparency is the opposite of secrecy. However, transparency should be assessed not only by the quantity of information provided-the quality is equally important. An excessive amount of information can actually make the information less accessible by hiding the most interesting data alongside other, less important data. Five broad criteria can be used to assess transparency: availability (ease of access, timeliness and clarity of presentation), reliability (quality of information), comprehensiveness (type, relevance and quantity), comparability (over time and between countries, requiring consistent methodologies) and disaggregation (level of detail of information).

　　Since 1966 the Stockholm International Peace Research Institute (SIPRI) has acted as an agent of transparency by collecting information from disparate open sources, and then analysing and presenting it in a way that is comprehensible to the general public. This short paper seeks to convey some of SIPRI's experiences in working with military expenditure and arms production data.