The rapid growth of bandwidth-demanding wireless technologies has led to the problem of spectrum scarcity. Cognitive radio technology promises a solution to the problem by allowing unlicensed users, access to the licensed bands opportunistically. This book evaluates the performance of the energy detection based spectrum sensing technique in noisy and fading environments. Both single user detection and cooperative detection situations were investigated. Closed form solutions for the probabilities of detection and false alarm were derived. The analytical results were veried by numerical computations using Monte Carlo method with MATLAB.