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A cross-layer optimization scheme combining retransmission with multiuser diversity is investigated for wireless communications. To this end, the joint design of adaptive modulation and coding (AMC) with the retransmission-based automatic repeat request (ARQ) protocol is first outlined. This design is then employed to devise multiuser scheduling schemes that can optimally capture the available multiuser diversity and retransmission-induced spectral efficiency gain. In addition, the proposed stochastic scheduling algorithms can operate even when the underlying fading channel distribution is unknown a priori while asymptotically converging to the optimum benchmark with guarantees on prescribed fairness and rate/delay requirements for a heterogeneous network traffic. Numerical results are provided to verify the advantage of these novel methods for multiuser transmissions over Nakagami block-fading channels.