If a conference paper is published as part of a book, use the same format as for a book or a book chapter.
Jones (1999) explained…
Wilkinson, R. (1999). Sociology as a marketing feast. In M. Collis, L. Munro, & S. Russell (Eds.), Sociology for the New Millennium. Papers presented at The Australian Sociological Association, Churchill, Victoria: Celts.
If the paper is published informally, include the month and year of the symposium in the reference.
Smith (2006) proposed...
Smith, P. (2006, March). How to make the most of the time you spend commuting. In M. Fox & P. Smith, Work-life balance in today's world Conference, London.
Conference proceedings (full)
If the proceedings are published in book form, follow the format for books.
Bickman and Ellis (1990) said that...
(Bickman & Ellis, 1990)
Bickman, L., & Ellis, H. (Eds.). (1990). Preparing psychologists for the 21st century: Proceedings of the National Conference on Graduate Education in Psychology, University of Utah, 1988. Hillsdale, NJ: L. Erlbaum.
If the proceedings are published regularly online, replace the publisher and place of publication with the URL.