Miniature conversion refers to the practice of altering the appearance of a miniature or model so as to deviate from the standard version purchased in a boxed set.

This practice is quite common amongst hobbyists who play miniature wargames such as The Lord of the Rings Strategy Battle Game, Warhammer Fantasy Battles and Warhammer 40,000, as well as many of the other games produced by Games Workshop. In these circumstances, conversions generally consist of combining "bitz" and modelling putty (known as "Green Stuff") to produce a new model with a unique appearance, which is generally a centrepiece of the player's collection, representing a powerful character or monster, or similar.

Some hobbyists convert (model) their miniatures for pure enjoyment, whereas sometimes they are forced to convert their miniatures to stay in line with the rules for their army (e.g., weapon changes, mounting miniatures on steeds) Some people spend more time converting their miniatures than painting them, and some hobbyists extensively convert every model in their army so that they can have a unique force. Some hobbyists will convert a model not for their army, but just as a way to clean out their "bitz box" and to have fun.