In this thesis I study the untwisted affine quantum algebras and their specialization at a primitive l-th root of unity. In particular my goal is the complete description of the center, when l is odd. The center of the specialization of the quantum algebra at odd roots of unity is already known in the finite case, that is for finite dimensional semisimple Lie algebras. In this thesis I prove that analogous results hold in the affine untwisted case.