A gamebook is a work of fiction that allows the reader to participate in the story by making effective choices. The narrative branches along various paths through the use of numbered paragraphs or pages. Gamebooks are sometimes informally called choose your own adventure books or CYOA, which is the title of one particular long and popular series by Bantam Books. Legally, Choose Your Own Adventure continues to be a trademark in current use.

There are three types of gamebooks. The first is the branching-plot novel (an example of this is the Choose Your Own Adventure series of gamebooks), which require the reader to make choices but are otherwise like a regular novel. The second type is the role-playing game solitaire adventure (an example of this is the Tunnels and Trolls series of gamebooks), which combines the branching-plot novel with the rules of a role-playing game, allowing the game to be played without a Gamemaster but requiring the purchase of separate manuals. The third type is the adventure gamebook (examples of these are the Fighting Fantasy and Lone Wolf series of gamebooks), which combines the branching-plot novel with a simple role-playing system unique to the book (or series). In all gamebooks, the story is presented as a series of text sections. Branching-plot novel sections often run to several pages in length, whereas RPG and adventure gamebook sections are usually no longer than a paragraph or two. At the end of a text section, the reader is usually given a choice of narrative branches that they may follow. Each branch contains a reference to the number of the paragraph or page that should be read next if that branch is chosen. The story continues this way until a paragraph or page which ends that branch of the story. In most RPG or adventure gamebooks, there is usually one "successful" ending, and the remainder are "failures." Branching plot novels, on the other hand, tend to be more concerned with narrative resolution rather than winning or losing, thus often have several endings with may be deemed "successful".
Gamebooks are typically written in the second person with the reader assuming the role of a fictional character. The titles are usually published in series containing several books, although individual gamebooks have also been published. While the books in many series are stand-alone narratives, others continue the narrative from the previous books in the series.