Multifuel, sometimes spelled multi-fuel, is a term applied to any type of engine, boiler, or heater or other fuel-burning device which is designed to burn multiple types of fuels in its operation. One common application of multifuel technology is in military settings, where the normally-used diesel or gas turbine fuel might not be available during combat operations for vehicles or heating units. However, the growing need to establish fuel sources other than petroleum for transportation, heating, and other uses has led to increased development of multifuel technology for non-military use as well.

A multifuel engine is constructed so that its compression ratio permits firing the highest octane fuel of the various accepted alternative fuels. A strengthening of the engine is necessary in order to meet these higher demands. Multifuel engines sometimes have switch settings that are set manually to take different octanes, or types, of fuel.

One common use of this technology is in the drive of military vehicles, so that they may run a wide range of alternative fuels such as gasoline or aviation (gas turbine) fuel. This is seen as desirable in a military setting as enemy action or unit isolation may limit the available fuel supply, and conversely enemy fuel sources, or civilian sources, may become available for usage.