Standard Definitionsis a work in progress; this is the second major edition. The American Association for Public Opinion Research plans to continue updating it, adding comparable definitions for other modes of data collection and making other refinements. AAPOR also is working with other organizations to further the widespread adoption and utilization of Standard Definitions. AAPOR is seeking the cooperation of companies that provide computer-assisted telephone interviewing (CATI) software. Some of those companies already have agreed to incorporate the definitions and formula into their software reports. AAPOR also is asking academic journals to use AAPOR standards in their evaluation and publication of articles; several, including Public Opinion Quarterly, already have agreed to do so. This report is one of several AAPOR publications. It is based on the work of an earlier committee headed by Tom W. Smith. Other AAPOR members who served on the committee include Barbara Bailar, Mick Couper, Donald Dillman, Robert M. Groves, William D. Kalsbeek, Jack Ludwig, Peter V. Miller, Harry O’Neill, and Stanley Presser. The current edition was edited by Rob Daves, who chaired a group that included Janice Ballou, Paul J. Lavrakas, David Moore, and Smith. Lavrakas led the writing for the portions dealing with mail surveys of specifically named persons and for the reorganization of the earlier edition. The group wishes to thank Don Dillman and David Demers for their comments on a draft of this edition. The AAPOR Secretariat will provide one (1) copy of this and other AAPOR publications at no additional cost (except for shipping and handling). After the first copy, copies are $2.50 each. Contact AAPOR at AAPOR-INFO@goAMP.com, or call (913) 310-0118. One may also view this and other AAPOR reports and documents on the Internet at http://www.aapor.org.