Prepared at the request of the AAPT Committee on Resource Letters; supported by a grant from the National Science Foundation.This is one of a series of Resource Letters on different topics, intended to guide college physicists to some of the literature and other teaching aids that may help them improve course contents in specified fields of physics. No Resource Letter is meant to be exhaustive and complete; in time there may be more than one letter in some of the main subjects of interest. Comments and suggestions concerning the content and arrangement of letters as well as suggestions for future topics will be welcomed. Such communications should be sent to Professor Arnold Arons, Chairman, Resource Letter Committee, Department of Physics, Amherst College, Amherst, Massachusetts.Notation:The letterEafter an item number indicates elementary level, useful principally for freshman liberal arts through sophomore physics courses; the letterIindicates intermediate (junior, senior) level; and the letterAindicates advanced material principally suited for senior, graduate study. An asterisk (*) indicates items particularly recommended for introductory study.Additional copies:Available from American Institute of Physics, 335 East 45 Street, New York, New York 10017. When ordering, request Resource Letter NS-1 and enclose a stamped return envelope.