A companion genre to steampunk, clockpunk and the like. Dieselpunk takes cultures that have reached the level of technology of the gas engine and electric power and create fantastical devices and events around giant mechanical walkers, robots, diesel-powered zeppelins, and rocket ships. Radio and other 'low-level' electronics are generally allowed, but not computers, TV, or other 'advanced' electronics. As a general rule, dieselpunk is based around the technological levels of the 1920s-1940s.
Because of the time period in question, dieselpunk often has one of the World Wars as a theme, or social alienation resulting from increased industrialization. On the other hand, the absence of the World Wars and the Great Depression may be used to explain the advanced development of industry and science along mechanical lines. It often includes themes common in pulp magazines and aethetics mirroring art deco. Being one of the Xpunk genres, it is common to have the stories be quite dark, sometimes violent, and have anti-hero protagonists; however, these 'punk' elements are not present as frequently as you might expect.
There is, of course, some debate over what true dieselpunk entails, but some works that might be included under the umbrella of dieselpunk include:
Steampunk :: Xpunk :: Atomicpunk