In this chapter, we investigate the problem of physical-layer security in wireless networks with cooperative relays. In Sections 11.2 and 11.3, we study the notion of deaf cooperation to reinforce security of transmission in wireless relay networks. We distinguish between two main approaches to deaf cooperation, namely, the cooperative jamming (CJ) approach and the noise forwarding (NF) approach. In a CJ scheme, a helping interferer transmits Gaussian noise when it can hurt the eavesdropper more than it can hurt the legitimate receiver, and hence improves the achievable secure information rate. The idea of introducing artificial noise in a Gaussian wiretap channel by a helper node was introduced in References 5-7. In relay networks with secrecy constraints, the role of CJ was further investigated, e.g., in References 8-10. References 11-13 proposed CJ strategies for multiple-antenna relay networks. On the other hand, in the NF scheme which was introduced in Reference 14, the relay node sends a dummy (context-free) codeword drawn at random from a codebook that is known to both the legitimate receiver and the eavesdropper to introduce helpful interference that would hurt the eavesdropper more than the legitimate receiver.