Irving Kaplansky (1917 - 2006) was a leading authority on algebra. He contributed greatly to the structure of Banach algebras, to locally compact groups and group representations. From 1945 to 1984, Professor Kaplansky taught mathematics at the University of Chicago, where he chaired the department from 1962 to 1967. In 1984 he became Director of the Mathematical Sciences Research Institute in Berkeley, California, a post he held until 1992. Irving Kaplansky received many awards and honors - among them, in 1989, the American Mathematical Society's Steele Prize. This book is a collection of 22 of his research papers. Each is followed up with new comments, often including references to later papers by other authors. In addition there are eight hitherto unpublished items. These cover a variety of topics and will be of interest to many readers.