You don't say anything is a saga of books. A saga is one long story involving many characters that takes place over a long period of time. 'War and Peace' and 'Gone with the Wind' are often called sagas. You could call the entire Harry Potter series a saga I suppose but people don't. It's not really saga-like - not enough characters, not a long enough time period.

Literally, the sagas were long, epic poems written in Iceland in the Middle Ages, containing histories of royal families and heroes and gods. By extension, a saga is usually a long literary work containing a multigenerational family history, and usually written in a serious style. I think "multigenerational" is the key, not the length of the series. Ken Follett's series of "Kingsbridge" books is called a "saga' because it deals with several family generations. British author John Galsworthy wrote a three-novel trilogy to which he gave the name "The Forsyte Saga" because it covers the story of several generations of the Forsyte family. Conversely, The Harry Potter series isn't a "saga" because it just deals with Harry Potter's life. Similarly, Patrick O'Brian's TWENTY-volume series of seafaring novels, the "Aubrey/Maturin" series, is not a saga because it just deals with the seafaring career of one person, Captain Aubrey.

Generally speaking, a saga is "a long, involved story, account, or series of events." The Harry Potter series is a set of books covering several adventures over the course of one boy's life at a wizarding school. Each book, in its own right, is a saga; as they are long and fairly involved tales covering one singular adventure per book. In other words, a series is "A set of events of a similar or related kind that follow one after another." I hope this helps, and good luck! :D

Thank you Clara.

It might offend purists for the reasons others have given, but using ‘saga’ to describe the Harry Potter books sounds natural. If you think they’re important, ‘series’ is too weak.