Leptospirosis is a widespread infection of man and animals, and locally it assumes considerable importance as a public health and economic problem. It is an important occupational infection among persons working with animals or in environments that may be contaminated by infected animals. In recent years, considerable attention has been devoted to this infection but efforts to control and eliminate it, especially from natural foci, are hindered by gaps in our knowledge. This memorandum is a review of recent progress and current problems in leptospirosis research, with special reference to taxonomy, epidemiological methods, and control measures. Certain aspects of the basic biology of leptospires that are relevant to these topics are also discussed.