"One Slayer fighting alone is formidable. Two is formidabler. Or… three? Mega-formidable. And after mega, it goes to mondo, then super, hyper, beaucoup d’crazy, stupid… it gets *exponentially* prefixy." - Buffy, Season 8
Comic books based on BtVS & Angel
Supplemental Buffyverse comics were published while Buffy and Angel were on the air. They expand on events and storylines from the show but are not considered canon by many fans. Joss was not involved in these storylines, but several writers and actors from the shows were. You can think of these as additional stories to be read at the conclusion of each season.
Continuation Buffyverse comics pick up the storylines where Buffy and Angel left off at their series finales. These are ongoing stories that are considered canon, as Joss has been directly involved. Most of them have been structured as seasons, with a timeline similar to a tv season and a complete story arc within each season. There are also several miniseries that tie in.