Writers in the social and behavioral sciences, along with those in the business and nursing fields, generally follow the guidelines set down by the American Psychological Association in their writing. These disciplines often rely on using the most current information, so parenthetical citation or signal phrases should include the publication date of the quoted source. When you use a source that does not include a date, you need to cite it differently to reflect that lack.
According to the "Publication Manual of the American Psychological Association" (6th edition, second printing), you should indicate the source of borrowed information with the author's last name and the year of publication in either a parenthetical citation or a signal phrase. When the book you cite has no publication date, you should indicate that by typing "n.d." instead (without the quotation marks), to indicate "no date." Such a citation might look like this: (Johnson, n.d.). If you use the author's name in a signal phrase, indicate the lack of a date in parentheses immediately following: According to Johnson (n.d.).
The References page entry for a book with no publication date follows the same guidelines as the entry for any book but uses "n.d." (without the quotation marks) instead of the year of publication. The entry begins with the author's last name, a comma and the first initial followed by a period. The lack of a date is indicated with "n.d." in parentheses with a period after the parentheses, as well. Then the title of the book appears, italicized, ending with a period. The city of publication appears next, followed by a colon and the publisher. Such an entry might look like this: Johnson, A. (n.d.). The Title of the Book (italicized). New York: Penguin. For an electronic book, include the publisher information if given but also add "Retrieved from" (without the quotation marks) and the URL or a DOI (digital object identifier) after the title. Electronic book entries do not have a period at the end.