Penny dreadfuls were cheap popular serial literature produced during the 19th century in the United Kingdom. The pejorative term is roughly interchangeable with penny horrible, penny awful, and penny blood. The term typically referred to a story published in weekly parts of 8 to 16 pages, each costing one penny. The subject matter of these stories was typically sensational, focusing on the exploits of detectives, criminals, or supernatural entities. First published in the 1830s, penny dreadfuls featured characters such as Sweeney Todd, Dick Turpin, Varney the Vampire, and Spring-heeled Jack.

The BBC called penny dreadfuls "a 19th-century British publishing phenomenon". By the 1850s, there were up to a hundred publishers of penny-fiction, and in the 1860s and 1870s more than a million boys' periodicals were sold per week. The Guardian described penny dreadfuls as "Britain's first taste of mass-produced popular culture for the young", and "the Victorian equivalent of video games".

While the term "penny dreadful" was originally used in reference to a specific type of literature circulating in mid-Victorian Britain, it came to encompass a variety of publications that featured cheap sensational fiction, such as story papers and booklet "libraries". The penny dreadfuls were printed on cheap wood pulp paper and were aimed at young working class men. The popularity of penny dreadfuls was challenged in the 1890s by the rise of competing literature, especially the half-penny periodicals published by Alfred Harmsworth.