The impact of wireless communication on our everyday life is of major significance. Wireless communication, despite the hype of the popular press, is a field that has been around for more than hundred years, starting around 1897 with Marconi's successful demonstrations of wireless telegraphy. Rapid progress in technology has also been around for quite a while. Wireless communication without any doubt is a paradigm shift, enabling multimedia communications between people and devices from any location. In an evolving Wireless World, there is demand of systems that possess great engineering challenge. It can be met only with efficient, reliable and robust Multi-user Wireless systems. This text emphasizes the Opportunistic Communication: a most recent technique used for enhancement of wireless systems performance in many ways. The book highlights the salient features of Opportunistic Communication and its benefit for utilizing it in Multiuser Scenarios. The book also covers advance topics such as Multiple Input Multiple Output (MIMO) Systems, Multiuser Diversity, Multiuser Beamforming and its exploitation in throughput enhancement of Wireless Networks.