In linguistics, zero derivation or, less frequently, null derivation is a derivation by means of the null morpheme or zero morpheme, i.e. changing the function of the word without changing its form. If the derivation changes the word class, it is also called a conversion.

Conversion is very common in the English language, as is illustrated by the conversion from telephone to to telephone, for example.

More recently, the Tivo corporation has sought to prevent the use of the conversion of the proper noun Tivo to the verb to Tivo (as in: don't forget to Tivo that show).