With the significant increase in demand for high data rate wireless systems, orthogonal frequency division multiplexing (OFDM) has been of particular relevance as it offers means to convey high data rates with low-complex transceivers in multipath channels. Therefore, security of data transmission over OFDM wireless systems is of paramount importance. In this book, we focus on the design of strategies that secure transmission with OFDM based wireless communications systems. In particular, this book capitalizes on information-theoretic characterizations of achievable secrecy rates for parallel Gaussian wiretap channels, when a legitimate transmitter (Alice) and a legitimate receiver (Bob) communicate in the presence of an eavesdropper (Eve) and friendly or unfriendly jammer. This book uses tools from optimization theory and game theory in order to design optimal or nearly optimal transmission strategies for secure and reliable wireless communications. This book contains a comprehensive framework with theoretical foundations and algorithmic solutions for researchers and engineers working on aspects of security of wireless communications.