Physical layer security in multiuser wireless networks focuses on secure communication without relying on higher-layer encryption. It leverages the inherent randomness of wireless channels to limit information accessible to eavesdroppers. Key approaches include designing transmit strategies without secret keys or generating secret keys via physical layer mechanisms. The field draws on information-theoretic security, starting with Shannon and Wyner's work, and extends to multiuser scenarios like broadcast, multiple-access, and interference channels. Techniques such as artificial noise, cooperative jamming, and secret-key agreement are used to enhance security. Game theory and stochastic geometry also contribute to secure communication strategies. Physical layer security can complement higher-layer encryption, offering provably unbreakable security. Recent research explores multi-antenna systems, relay networks, and cooperative methods to improve secrecy. Challenges include eavesdropper CSI, channel fading, and ensuring secure communication in dynamic environments. The paper surveys these advancements, highlighting future research directions in secure wireless networks.Physical layer security in multiuser wireless networks focuses on secure communication without relying on higher-layer encryption. It leverages the inherent randomness of wireless channels to limit information accessible to eavesdroppers. Key approaches include designing transmit strategies without secret keys or generating secret keys via physical layer mechanisms. The field draws on information-theoretic security, starting with Shannon and Wyner's work, and extends to multiuser scenarios like broadcast, multiple-access, and interference channels. Techniques such as artificial noise, cooperative jamming, and secret-key agreement are used to enhance security. Game theory and stochastic geometry also contribute to secure communication strategies. Physical layer security can complement higher-layer encryption, offering provably unbreakable security. Recent research explores multi-antenna systems, relay networks, and cooperative methods to improve secrecy. Challenges include eavesdropper CSI, channel fading, and ensuring secure communication in dynamic environments. The paper surveys these advancements, highlighting future research directions in secure wireless networks.