Like unpublished interviews, letters do not need to be listed in a references page. Instead, cite the information in the text of your document, according to the following format:

(C. Jones, letter, June 6, 1984)

Here the entry consists of the first initial and last name of the letter writer, the type of communication, and the date.

For more specific information, consult the Publication Manual of the American Psychological Association (Fifth Edition).