Cletus
- Says he is definitely the same person as Anencletus.
- http://www.1911encyclopedia.org/Cletus

Catholic Online: St. Cletus
- Short biography.
- http://www.catholic.org/saints/saint.php?saint_id=610

Cletus, Pope
- Brief biography.
- http://www.saintpatrickdc.org/ss/0426.htm#clet

Anacletus
- Brief article this pope, by Karen Rae Keck.
- http://www2.evansville.edu/ecoleweb/glossary/anacletus.html

Popes Through the Ages: St. Cletus
- Short note on this pope and the difficulty over his name.
- http://www.cfpeople.org/Books/Pope/POPEp3.htm

Catholic Encyclopedia: Pope St. Cletus
- Says that "Cletus" is only another form of "Anacletus", briefly explains how the error of thinking the two names are two different popes came about, says that Cletus died in about 88.
- http://www.newadvent.org/cathen/04054a.htm

Catholic Encyclopedia: Pope St. Anacletus
- Pope St. Anacletus, third pope, a martyr, d. about 91. "Whether he was the same as Cletus, who is also called Anencletus as well as Anacletus, has been the subject of endless discussion."
- http://www.newadvent.org/cathen/01446a.htm