James Bartholomew Jimmy Olsen is a fictional character, a photojournalist who appears in DC Comics’ Superman stories. An anonymous "copy boy" who resembles Olsen makes a brief appearance in Action Comics #6, but the character as we know him first appeared in the radio show, The Adventures of Superman, on April 15, 1940. The character moved from the radio show into the comics in 1941, first appearing in Superman v1 #13 (1941). Along with his appearances in current Superman titles (Superman and Action Comics), he is one of the main protagonists in DC Comics' weekly series Countdown, with a super heroic alter-ego called Mr. Action.

Jimmy is traditionally depicted as a bow tie-wearing, red-haired young man who works as a cub reporter and photographer for The Daily Planet, alongside Lois Lane and Clark Kent, whom he idolizes as career role models. In most depictions of the character, he also has a strong friendship with Superman. As Superman's friend, Jimmy has special access to the Man of Steel, thanks to Superman's gift to Jimmy of a "signal watch," a wristwatch which, with the press of a button, emits a special ultrasonic frequency signal that Superman can hear anywhere on Earth. (In Post-Crisis continuity Jimmy invented the watch himself, and Superman briefly considered confiscating it. In New Earth continuity, the watch was designed by Superman based on a larger signalling device Jimmy created.)

In many Silver Age comic books, Jimmy was often seen sharing adventures with Superman, who saved him from various predicaments ranging from dangerous to merely embarrassing. This was particularly pronounced in the series Superman's Pal Jimmy Olsen (published from 1954 to 1974), which saw Olsen in a variety of slapstick adventures and strange transformations. Like most DC characters, modern portrayals of Olsen have been more serious in tone.

An important part of the Superman mythos, Jimmy Olsen has appeared in most other media adaptations of the character.