An American comic book is a thin periodical originating in the United States, on average 32 pages, containing comics. While the form originated in 1933, American comic books first gained popularity after the 1938 publication of Action Comics, which included the debut of the superhero Superman. This was followed by a superhero boom that lasted until the end of World War II. After the war, while superheroes were marginalized, the comic book industry rapidly expanded and genres such as horror, crime, science fiction and romance became popular. The 1950s saw a gradual decline, due to a shift away from print media in the wake of television and the impact of the Comics Code Authority. The late 1950s and the 1960s saw a superhero revival and superheroes remained the dominant character archetype throughout the late 20th century into the 21st century.

Comics are a medium used to express ideas with images, often combined with text or other visual information. It typically takes the form of a sequence of panels of images. Textual devices such as speech balloons, captions, and onomatopoeia can indicate dialogue, narration, sound effects, or other information. There is no consensus among theorists and historians on a definition of comics; some emphasize the combination of images and text, some sequentiality or other image relations, and others historical aspects such as mass reproduction or the use of recurring characters. Cartooning and other forms of illustration are the most common image-making means in comics; Photo comics is a form that uses photographic images. Common forms include comic strips, editorial and gag cartoons, and comic books. Since the late 20th century, bound volumes such as graphic novels, comic albums, and tankōbon have become increasingly common, along with webcomics as well as scientific/medical comics.