The book in hand is the result of converting the idea of cognitive radio in satellite communications. A major part of the book has resulted from the outcome of the research done by author. This book covers many aspects of cognitive radio based satellite communications, specially issues related to spectrum sensing. This book starts with introduction of satellite communications and the role of cognitive radio for spectrum sensing in satellite communications. We introduce a framework to study the probability of error in sensing the spectrum. We also discuss cooperative spectrum sensing along with throughput and energy consumption in a cognitive radio based satellite network. The derived analytical results in this book will help in the study of performance of cognitive wireless systems, which have found useful applications in spectrum sensing in satellite communications. This book will be useful to academicians and researchers who want to explore the ideas of cognitive radios in satellite communications.