When you quote forty or more words, set off the quotation by indenting it one-half inch from the left margin. Use the normal right margin and do not single-space.

Long quotations should be introduced by an informative sentence, usually followed by a colon. Quotation marks are not necessary because the indented format tells readers that the words are taken directly from the source.

Yanovski and Yanovski (2002) have described earlier treatments of obesity that focused on behavior modification:

With the advent of behavioral treatments for obesity in the 1960s, hope arose that modification of maladaptive eating and exercise habits would lead to sustained weight loss, and that time-limited programs would produce permanent changes in weight. Medications for the treatment of obesity were proposed as short-term adjuncts for patients, who would presumably then acquire the skills necessary to continue to lose weight, reach “ideal body weight,” and maintain a reduced weight indefinitely. (p. 592)

Notice that at the end of an indented quotation the parenthetical citation goes outside the final mark of punctuation. (When a quotation is run into your text, put the parentheses before the final mark of punctuation. See the example here.)