Physical Layer Security (PLS) has emerged as a promising and powerful concept for securing future wireless technologies including 5G and beyond networks as it has the potential to solve many of the problems associated with conventional cryptography-based approaches. In this chapter, the principles of PLS as a complementary solution to cryptography for future networks are presented. The concepts, merits, and demerits for different types of PLS techniques are discussed and explained. Moreover, the recent applications of PLS to different emerging wireless technologies are also presented. Furthermore, the details about physical layer authentication methods against spoofing attacks and details about jamming attacks and related solutions are also included.