Cooperative multiple-input multiple-output (CMIMO) is a form of cooperative communications. CMIMO emulates the functionality of multi-antenna systems by grouping wireless devices to operate as virtual multi-antenna nodes. Its main objectives are to boost network throughput, conserve energy, and improve network coverage. In this article, we discuss recent applications of CMIMO in contemporary wireless networks, including wireless sensor, mobile ad hoc, wireless LAN, cognitive, and cellular networks. We first review CMIMO techniques at the physical layer. We then focus on state-of-the-art approaches for realizing CMIMO at the network layer, and classify these approaches based on their objectives and application scenarios, and how they exploit CMIMO gains. We highlight several open issues that present challenges to practical deployment of CMIMO.