The Oriental bees of the genus Ceratina Latr. are difficult to identify. Until now our knowledge of these insects consisted mainly of a considerable number (about 90) of isolated descriptions, scattered through several scientific journals. Most of these descriptions are based on colour characters and although these are certainly not without taxonomic value, they must be used with great care on account of their intra-specific variability. The structural and sculptural characters which are much more reliable for distinguishing the species have thus far not received sufficient attention. There exist a few keys, dealing with the species occurring in certain parts of the region, but none of these contains more than 11 species and the characters used are often of doubtful taxonomic value. An attempt to identify a large number of species collected in Indonesia, mainly in Java, by Dr. and Mrs. Lieftinck, my wife and myself, soon demonstrated the necessity of a revision of the Ceratina species described from this and other parts of the Oriental region. It would have been completely impossible to recognize the majority of these species with sufficient certainty from their descriptions. Fortunately I had an opportunity to study much authentic material. In September 1951 I examined the types of several species described by Smith, Cameron, and Cockerell in the collections of the British Museum (Natural History) and the Oxford University Museum ; some additional types, preserved in the Rothney collection in the latter Museum, were kindly sent to me for study at a later date. The U.S. National Museum sent me a very interesting collection of oriental Ceratina, containing several species identified by Cockerell as well