Ammonium molybdate is an odorless crystalline compound ranging in color from white to yellow-green. Also called molybdic acid hexammonium salt tetrahydrate, ammonium molybdate tetrahydrate and ammonium heptamolybdate tetrahydrate. In chemistry a Ammonium molybdate is a compound containing an oxoanion with molybdenum in its highest oxidation state of 6. Ammonium molybdate can form a very large range of such oxoanions which can be discrete structures or polymeric extended structures, although the latter are only found in the solid state.

The discrete Ammonium molybdate oxoanions range in size from the simplest MoO42−, found in potassium molybdate up to extremely large structures found in isopoly-molybdenum blues that contain for example 154 Mo atoms.