Ammonium phosphate is the salt of ammonium and phosphate. It is a highly unstable compound with the formula (NH₄)₃PO₄. Because of its instability, it is an elusive and of no commercial value (except for scientific research). In addition to (NH₄)₃PO₄, a related double salt (NH₄)₃PO₄.(NH₄)₂HPO₄ is also recognized. It too is unstable. The instability of these salts results of their facile decomposition with evolution of ammonia:

(NH₄)₃PO₄ → H(NH₄)₂PO₄ + NH₃

In contrast to the fragile nature of the triammonium salts, diammonium phosphate (H(NH₄)₂PO₄) is a valuable material, mainly used as a fertilizer.