The paper describes the principles involved in the application of coincidence counting to problems in nuclear physics, and gives details of the various methods of approach to the solution of nuclear level schemes, with some of the difficulties encountered. It is shown that the maximum source strength which can be used is inversely proportional to the coincidence resolving time and that the method of experiment has the great advantage over most other methods in that it can be used with very weak sources (sources having an activity of about 10−5millicurie). An accurate knowledge of the absolute net efficiency of a Geiger counter for all types of radiation is required in the interpretation of the coincidence rates, and the method of achieving this at the same time as information is obtained about nuclear level schemes is explained. Further, it is pointed out that the method makes possible a simple and rapid determination of the total energy of disintegration of &bgr;‐radioactive nuclei and therefore of the mass differences between parent and daughter nuclei.