Deadlands is a genre-mixing alternate history role-playing game which combines the Western and horror genres, with some steampunk elements. The original game was written by Shane Lacy Hensley and published by Pinnacle Entertainment Group in 1996.

The eight-time Origins Award–winning setting has been converted to many other systems over the years and is available in the original Classic Rules, the revised Classic Rules, d20 System and GURPS adaptations, and a Savage Worlds version called Deadlands: Reloaded.

Shane Lacy Hensley had the idea for a new game focusing on cowboys and zombies in 1994 as he was setting up his company Pinnacle Entertainment Group, when he saw a painting by Brom of a Confederate vampire on the cover of White Wolf Publishing's soon-to-be released Necropolis: Atlanta supplement; he then began writing the game that became Deadlands, and after completing a first draft, Hensley flew in two game designer friends of his, Greg Gorden and Matt Forbeck, and both of them liked the game enough that they asked to buy into Pinnacle.

The game is set in the United States in the last quarter of the 19th century. The canonical year for the first edition of Deadlands is 1876. A later supplement, Tales o' Terror, advances the game's backstory and metaplot ahead one year, to 1877. The second edition of Deadlands uses the updated backstory of 1877 as the canonical starting point. Deadlands: Reloaded further updates the backstory and advances the canonical starting point to 1879.

The basic rules provide for characters and settings that could be expected to appear in the "Wild West" genre of movies and pulp fiction, and most of the in-game action is presumed to occur in the wild frontiers of the American West, or in barely tamed frontier towns like Tombstone, Arizona or Dodge City, Kansas. However, later supplements expanded the in-game adventuring area to include places such as the Deep South, the Mississippi River, Mexico, and the Northeastern United States. These supplements often provide for adventures set in urban areas such as New Orleans, New York City, or Boston.

The canonical, basic setting is referred to as the "Weird West" due to the juxtaposition of the Western setting with the horrific and fantastical elements of the game. The history of the Weird West is identical to real-world history, up until July 3, 1863. On this date in the game, a group of American Indians from various tribes, led by a Sioux shaman known as "Raven," performed a ritual in an effort to drive out the European settlers. This ritual created a conduit to a spiritual realm populated by powerful malicious entities known as the "Reckoners". The events surrounding and immediately subsequent to Raven's ritual is known as "The Reckoning".

The Reckoners feed on negative emotions, particularly fear. Sufficient levels of fear in the population of a given location allow the Reckoners to begin subtly altering the environment of that location: the sun shines a little less brightly, trees become stunted and "evil" looking, rock formations take on the appearance of corpses or monsters, and so on. The more powerful the fear, the greater the environmental changes.

The ultimate goal of the Reckoners is to turn the entire Earth into an evil, haunted wasteland — literally a Hell on Earth. However, the Reckoners cannot directly enter Earth's realm unless the overall fear level of the entire planet becomes sufficiently high. To this end, they use their powers to create monsters, madmen, zombies, and other creatures and villains that will sow fear and terror throughout the land.