A provitamin is a substance that may be converted within the body to a vitamin. The term "previtamin" is a synonym. For example, "Provitamin B5" is a name for panthenol, which may be converted in the body to vitamin B₅ (pantothenic acid).

The term "provitamin" is used when it is desirable to label a substance with little or no vitamin activity, but which can be converted to an active form by normal metabolic processes. For example, "provitamin A" is a name for β-carotene, which has only about 1/6 the biological activity of retinol (vitamin A); the body uses an enzyme to convert β-carotene to retinol. In other contexts, both β-carotene and retinol are simply considered to be different forms (vitamers) of vitamin A.