Abstract M-PSK cooperative trellis codes are proposed for two-user coordinate interleaved coded cooperation operating over quasistatic Rayleigh fading channels. The coding approach properly combines cooperative and modulation diversity techniques to take their full advantage. Two selective cooperation schemes are considered related to whether users know the cooperation status or not. Upper bounds on the pairwise error probability of the considered schemes are derived for each cooperation case which lead to new code design criteria. Based on these criteria, 4-, 8-, 16-state QPSK and 8-, 16-state 8PSK cooperative trellis codes are obtained by means of exhaustive computer search. The error performance evaluation of the new codes by computer simulations shows that they outperform the corresponding best space-time codes used in cooperation with coordinate interleaving.