We present medium access controllers (MAC) for ad-hoc networks which include uplink and downlink multi-user physical layer models as well as multiple antennas. We note the advantages of these MACs over those in the literature, including a multi-antenna version of the CSMA/CA protocol used in the distributed coordination function (DCF) mode of the IEEE 802.11 MAC. Specifically, our MAC is among the first to explicitly consider multi-user techniques in an ad-hoc network, which results in superior rate performance. We include interference and network topology in the design of our protocols. We characterize MAC controllers in terms of transport capacity, and present numerical results which show the benefit of multi-user techniques in the physical layer.