Mary Jane Watson, often is shortened to MJ, is a fictional supporting character appearing, originally, in Marvel comic books and, later, in multiple spin-offs and dramatisations of the Spider-Man titles as the best friend, love interest, and, in some continuities, wife (as Mary Jane Watson-Parker) of Peter Parker, the alter ego of the title character. Created by writer Stan Lee and artist John Romita, Sr., after a few partial appearances and references, her first full appearance was in The Amazing Spider-Man #42 (November 1966).

She is depicted as an extremely beautiful, green-eyed redhead, and has been the primary romantic interest of Peter Parker for the last twenty years, although initially competing with others for his affection, most prominently with Gwen Stacy and the Black Cat. Mary Jane's relatively unknown early life was eventually explored in Amazing Spider-Man' #259.

Today, Mary Jane is considered an important part of the Spider-Man series and has been featured in most other media adaptations of the character. She has even been the main character of some comics and novels aimed at young female readers. Perhaps most notably, MJ, portrayed by Kirsten Dunst, played a key role in the recent film series. Currently, Evan Rachel Wood is attached to play Mary Jane on Broadway in the new musical, Spider-Man: Turn Off the Dark.