Free Comic Book Day is a day when participating comic stores give away certain issues of comics for free to their patrons. This event is spearheaded by the comic book industry in North America, although stores all over the world are welcome to participate, and it tends to attract a great deal of media attention. By tradition, Free Comic Book Day occurs on the first Saturday in May after a major comic book related or superhero based film is released.

The first Free Comic Book Day was held in 2002, with several goals. It was meant to promote comics to new readers while appealing to old readers to return to the genre, and also to thank long-time comic consumers. Each year, Free Comic Book Day is organized by Diamond Comic Distributors, a major distributor of comics in North America, which coordinates with publishers to offer selected editions of comics at very low cost to store owners.

While the comics chosen for Free Comic Book Day are not free for the store owners, the cost is kept low enough that giving the comics away for free is feasible. Participating stores generally agree to carry at least 10 of the comics designated for Free Comic Book Day, with other titles being available for those who want them, including special editions produced specifically for Free Comic Book Day. Some store owners also choose to discount other merchandise for customers who come in on Free Comic Book Day.

Store policies on Free Comic Book Day vary. Some stores only hand out one comic per customer, while others allow customers to choose several of the free comics on offer. Not all comic book stores participate, either: for a list of participating stores, people can search the web for “free comic book day” and their area, or ask their local independent bookseller or comics store if they are participating. Stores which haven't planned on participating might change their minds if they sense enough public interest.

Some critics of Free Comic Book Day have pointed out that it focuses primarily on the output of major comic book companies, rather than smaller, independent publishing houses. However, the hope is that once people start reading comics and frequenting a comic book store, they will grow interested in offerings from lesser known publishers and authors, making Free Comic Book Day a promotion for all sorts of comics, not just the products of publishers like Marvel and DC. Many smaller publishers and distributors cannot afford to offer their products at low cost, which makes it financially impractical for them to be included in Free Comic Book Day.