Synopsis Considerable advances have been made in the systematics of the fishes of India and the neighbouring countries since the publication of F. Day's Fishes of India (1878) and his two volumes on Fishes in the Fauna of British India series (1889). With the introduction of the International Rules of Zoological Nomenclature, several of the generic and specific names as found in Day's works have become invalid. Furthermore, due to classificatory changes many of the families as given in Day are now split up. For example, the Siluridae of Day now consists of the families Ariidae, Plotosidae, Siluridae, Bagridae, Amblycepitidae, Akysidae, Sisoridae, Chacidae, Schilbeidae, Saccobranchidae, Clariidae, and Olyridae. The same may be said with regard to many of the composite genera and species found in Day. Thus, Day's books, while remaining important landmarks in Indian ichthyology, especially with regard to the description and illustration of the majority of the species, are not to-day of much practical use to the student of ichthyology. In order to bridge over the nomenclative and classificatory deficiencies in Day's works, Dr. K.S. Misra undertook, in 1946, the preparation of the series of the "Check Lists" and "Aids" on the Fishes of India, Burma, and Ceylon. Besides a deep knowledge of fish taxonomy, this laborious work required an intimate knowledge of the rules and procedure of taxonomy and of the taxonomic literature. Dr. Misra has published so far two parts of each of the series mentioned above. As the preparation of this comprehensive type of work for the remaining fishes of India, Burma, and Ceylon would take considerable time, it was felt that if "An Aid to the Identification of the Common Commercial Fishes of India and Pakistan" be prepared, with the scientific names of the fishes standardised and classified, it would solve, to a great extent, the urgent need keenly felt by many students of Indian fishes and by those engaged in practical fisheries work. The Indo-Pacific Fisheries Council of the Food and Agricultural Organisation of the United Nations has also suggested the preparation of such regional Keys and Aids for the Indo-Pacific area. The preparation of such an Aid was entrusted, in 1954, to Dr. K.S. Misra, Assistant Superintendent, Zoological Survey of India, who has now completed it. It is hoped that it will be of considerable practical use to fisheries workers and students of systematic ichthyology.