Abstract. We prove a functional equation for two projective systems of finite abelian p-groups, {an} and {bn}, endowed with an action of Z d p such that an can be identified with the Pontryagin dual of bn for all n.Let, unramified outside a finite set of places. Let A be an abelian variety over K. We prove an algebraic functional equation for the Pontryagin dual of the Selmer group of A.