In this paper we address the major physics principles and the engineering issues associated with the implementation of a Heavy Ion Beam Diagnostic for ITER for the edge measurements of the plasma electric and poloidal magnetic fields. Two diagnostic configurations are compared: i) a system based on a Tl+ ion beam controlled by a set of electrostatic steering plates and an energy analyser as detector and ii) another one based in the injection of Au0 atoms and a multiple cell array detector with time of flight measurement capability. The ions' trajectories and attenuations were calculated by dedicated simulation codes using the relevant ITER equilibrium parameters. Estimations of measurement accuracy are presented for a chosen configuration.