This paper provides a comprehensive review of physical layer security in multiuser wireless networks. The fundamental principle of physical layer security is to enable confidential message exchange over a wireless medium without relying on higher-layer encryption. This can be achieved through intelligent transmit coding strategies or by exploiting the wireless communication medium to generate secret keys over public channels. The survey begins with an overview of information-theoretic security, tracing its evolution from Shannon and Wyner's pioneering work to modern multi-antenna systems. It covers secure transmission strategies for various network types, including broadcast, multiple-access, interference, and relay networks. The paper also discusses secret-key generation and establishment protocols, channel coding design for secrecy, and interdisciplinary approaches based on game theory and stochastic geometry. Additionally, it addresses physical layer message authentication and highlights potential research directions in this area. The introduction emphasizes the challenges posed by the broadcast nature and superposition of wireless signals, and the limitations of traditional cryptographic methods. The fundamentals of secrecy, including performance metrics and the wiretap channel, are detailed, followed by an exploration of single-antenna and multi-antenna wiretap channels. The survey then delves into multi-user networks, focusing on broadcast, multiple-access, and interference channels, as well as relay and cooperative methods. The paper concludes with a discussion of future research directions and references to recent monographs for further reading.This paper provides a comprehensive review of physical layer security in multiuser wireless networks. The fundamental principle of physical layer security is to enable confidential message exchange over a wireless medium without relying on higher-layer encryption. This can be achieved through intelligent transmit coding strategies or by exploiting the wireless communication medium to generate secret keys over public channels. The survey begins with an overview of information-theoretic security, tracing its evolution from Shannon and Wyner's pioneering work to modern multi-antenna systems. It covers secure transmission strategies for various network types, including broadcast, multiple-access, interference, and relay networks. The paper also discusses secret-key generation and establishment protocols, channel coding design for secrecy, and interdisciplinary approaches based on game theory and stochastic geometry. Additionally, it addresses physical layer message authentication and highlights potential research directions in this area. The introduction emphasizes the challenges posed by the broadcast nature and superposition of wireless signals, and the limitations of traditional cryptographic methods. The fundamentals of secrecy, including performance metrics and the wiretap channel, are detailed, followed by an exploration of single-antenna and multi-antenna wiretap channels. The survey then delves into multi-user networks, focusing on broadcast, multiple-access, and interference channels, as well as relay and cooperative methods. The paper concludes with a discussion of future research directions and references to recent monographs for further reading.