Mules are a type of shoe that is backless and often closed-toed. They can be any heel height from flat to high. This style of shoe is predominantly worn by women but some styles for men are also available. Historically, Mules were an indoor shoe style and were often associated with prostitutes. Marilyn Monroe, among others, in the early 1950's is given credit for moving the mule into outdoor wear and helped to break the shoe's poor reputation. Mules experienced some popularity in the 1950's and early 60's, and were seen in 1970s almost exclusively in the form of open-back Scandinavian clogs, but then re-emerged in the early 1990's, especially in its open-toed form (the "slide"), and has begun to dominate the shoe market for women.

The term is generally believed to have been derived from the ancient Roman calceus mulleus, a red shoe worn by senators and other high officials, although there is little indication of any structural resemblance. At any rate, it has nothing to do with sterile hybrid equids.