As a result of the world facing an information technology and communication revolution, more technologies evolved and a massive increase in the number of devices and sensors connected to the Internet occurred. This caused the need for a freer spectrum, reliable wired or wireless connections as well as secure and reliable channels of communication.CR is an intelligent wireless communication technique, which realizes its surroundings in all cases. It was first proposed by Joseph Mitola which suggested using CR to make the best use of the available spectrum and to increase productivity.In this book, we will be evaluating the efficacy of narrow band spectrum sensing in Cognitive Radio by surveying and comparing some methods proposed before we propose our work in chapter three. Also, this book deals with two important problems that encounter the spectrum sensing and offers solutions to these problems.