Comic books are good entertainment, and have told countless stories over the years, but to many their value goes well beyond the stories contained inside. As with many other items like stamps and baseball cards, there’s a large market for collecting comic books. And like with other collectibles, there are a few things that will help drive up the value of any given comic book.

Like with other valuables, age is a major factor. Older comic books, naturally, are harder to find than what you’d find right on the shelf. And the rarer something is, the more valuable it’s going to be simply by scarcity. Just as important as age is condition. Nobody will pay money for a copy of Amazing Fantasy #15 if it’s falling apart, but if it’s been properly preserved, an older comic is going to be very valuable.

The content of the issue in question can also be a major deciding factor in the value of a comic book. What a collector is going to look for is either the first appearance of a major character or a major turning point in that character’s story. For example, a comic depicting the first appearance of a hero like Wolverine or Spider-Man is going to be worth quite a bit. By contrast, one-shot appearances by minor villains, or low quality stories, aren’t going to be considered worth collecting. And, naturally, the more prestigious the character involved, the more valuable it’s going to be. The first appearance of an iconic character like Spider-Man, for example, is going to be worth more than a lesser known character such as Luke Cage or Iron Fist.

So what are the most valuable comic books in the world?

Amazing Fantasy #15, the first appearance of Spider-Man, is estimated to be valued at around $42,000. That’s a big jump over its original selling price of around 12 cents in 1962. What’s mainly driving this comic’s price up is the aforementioned wall crawler, who changed the face of comic book heroes. Peter Parker was the first superhero to really have the same sorts of real life problems that many of his readers did, and thus identified more with his audience. This has been a major influence of nearly every comic book hero that’s come out since.

From DC comics, the first appearance of Batman is a major contender for most valuable comic. A high quality issue of Detective Comics #27 is estimated to be worth over $300,000 – well over its cover price of 10 cents in 1939. The caped crusader is one of the most recognizable comic characters in the world, so naturally his first appearance is going to be worth the big bucks.

But by far the most valuable comic book is Action Comics #1, the original appearance of the Man of Steel, Superman himself. Considered by many to be the original superhero, Superman is what people think of when they think comic books. Some estimate that a good copy of the original comic book is worth over $350,000, and one owner of such a copy is rumored to have turned down an offer of $2 million for it.

Comic books can be valuable collector’s items, if you know what to look for. The most valuable comics are the old ones in good condition, which have iconic characters or events in them. So if you’ve got some vintage comics, it pays to keep good care of them.