A connection system of piping for distribution systems of pressurized or depressurized fluids, the system including: —a connection joint having an insertion portion insertable in the piping so as to seal it and a retention portion, projecting therefrom when the joint is inserted therein; —a retainer suitable to longitudinally retain the connection joint to the piping, said retainer including: i) a retention element which engages the retention portion for constraining the joint longitudinally; and ii) clamping element adapted to exert a clamping force to lock the retention element to the piping.