This paper considers protocols for fading, wireless relay networks that aim to achieve cooperative diversity through the use of distributed space-time codes. All point-to-point communication is modeled as taking place over quasi-static, Rayleighfading channels with each node in the network operating in halfduplex mode. Channel-state information is assumed to be present only at the receiver. The diversity-multiplexing gain tradeoff (DMT) is taken to be the measure of performance. Prior work in this area relating to the identification of the DMT of various protocols as well as to DMT-optimal code construction is first reviewed. This is followed by a description of our recent results in this area. These include determination of the DMT of the orthogonal amplify-and-forward and selection decodeand-forward protocols as well as some simply-described, DMT-optimal code constructions based on cyclic division algebras.