While some argue that American Psychological Association "rules" started with the birth of the organization in 1892 (Evans et al., 1992), most sources agree that the first style guide came out in 1929. Sliced bread is only one year older! The first set of clearly published rules was just seven pages long (Bentley et al., 1929). These rules were augmented and revised for several decades before the APA leaders realized they needed to start numbering their guides as "editions." As you may expect, the formatting, citation, and referencing rules have undergone many changes over the last years. The current edition is the 7th, which was published in October 2019, although it is labeled as 2020.
As you work around your reflexes of wanting to still use 6th edition rules or even inserting MLA (do not mix styles), you might find some of the changes to be refreshingly simplifying, such as a less complicated running head and no longer needing to figure out the city and state where book publishers are located. This coupled with the fact that many facets remain the same should make your transition not too difficult.
If you do not own the manual itself, you may like to put this link on your favorites, because no tutorial covers absolutely everything, of course: https://apastyle.apa.org.
Thank you for your curiosity. You can begin the tutorial by clicking the button below. Please make sure you check the "review" lists on these pages, too: while this tutorial assumes you have been working with 6th edition, there may be some things that you previously missed. On the last page you will find a link to the self-test and another to a help site that has more information you might like to add to your browser's favorites list.
If you feel confident you already know the rules, take this 25-question test to check your knowledge. (This is the same test linked at the end of the tutorial for those who wish to learn first.)
Bentley, M., Peerenboom, C. A., Hodge, F. W., Passano, E. B., Warren, H. C., & Washburn, M. F. (1929, February). Instructions in regard to preparation of manuscript. The Psychological Bulletin, 26(2), 57-63.
Evans, R. B., Sexton, V. S., & Cadwallader, T. C. (1992). The American Psychological Association: A historical perspective. American Psychological Association.