Multiple Input Multiple Output (MIMO) systems are becoming the inherent part of all future wireless systems including 3GPP, IEEE 802.11n, LTE, LTE advanced and Cognitive radio systems. The hardware complexity problem of MIMO systems is addressed by the concept of Antenna Selection (AS) in which subset of antenna is selected at the transmitter or receiver based on the Channel State Information (CSI). This book initially provides a brief scientific background for Transmit AS(TAS) system based on Maximal Ratio Combining (MRC) and the simulation framework for end-to-end TAS/MRC system with advancements in channel designs and feedback models. Further, a multiple TAS system and its performance under various fading channels are presented. The concept of Aggregate Interference (AI) and characterization of AI for different interference scenario by using stochastic geometry tools is prsented for Cognitive Radio Network (CRN). The outage probability and ergodic capacity of the CRN network is derived for TAS based MIMO system.This book provides the analytical and simulation based presention of the fundamental concepts of AS in MIMO system for future generation wireless sysytems