Originally published by the Bureau of Fisheries of the U. S. Department of Commerce in 1922, this may be the only book ever published on the operation of commercial aquariums. At the time of original publication the author, Charles Haskins Townsend was Director of the New York Aquarium. The writer has had long experience in the management of the aquarium in New York City and has assisted in planning certain aquariums already built as well as others projected. He was connected with the National Commission of Fisheries during the period when that organization maintained temporary aquariums at the great industrial exhibitions held in this country and observed some of them in operation. Millions of people saw those aquariums of the past, while other millions enjoy the few that exist here at present. Having supplied information recently to a score of cities that contemplate constructing aquariums, the writer has felt it incumbent upon him to set forth the essentials of the matter for the guidance of an increasing number of inquirers. The present discussion is based largely on the methods of the large aquarium in New York City, which has been in operation for 30 years and is now undergoing extensive modernization.