Central bank transparency has become the topic of a lively public and academic debate on monetary policy. Unfortunately, it has been complicated by the fact that transparency is a qualitative concept that is hard to measure. This paper proposes a comprehensive index for central bank transparency that comprises the political, economic, procedural, policy and operational aspects of central banking. The index is compiled for nine major central banks. It is based on a detailed analysis of actual information disclosure and reveals a rich variety in the degree and dynamics of central bank transparency.