We study the multiple antenna half-duplex relay channel from the diversity-multiplexing tradeoff (DMT) perspective. We find performance upper bounds and show that compress-and-forward (CF) protocol achieves the upper bound. We argue that although it is hard to find the exact DMT expressions for decode-and-forward (DF) type protocols, they would be suboptimal in the multiple antenna case. We also study the multiple-access relay channel (MARC), and evaluate how CF works in this system. Our results show that CIF is a robust strategy, which performs well in different relay networks and multiple antenna scenarios.