A nitrous oxide engine, or nitrous oxide system is an internal combustion engine in which oxygen for burning the fuel comes from the decomposition of nitrous oxide, N2O, as well as air.

Nitrous oxide, commonly referred to as laughing gas, along with various street names, is an inert gas which can induce euphoria, dissociation, hallucinogenic states of mind, and relaxation when inhaled.

Nitrous oxide fuel blend propellants are a class of liquid rocket propellants that were intended in the early 2010s to be able to replace hydrazine as the standard storable rocket propellent in some applications.