Social Internet of Things is a new paradigm where Internet of Things merges with Social Networks, allowing people and devices to interact, facilitating information sharing and enabling a variety of at-tractive applications. However, face to this new paradigm, users remain suspicious and careful. They fear disclosure of their data and violation of their privacy. Without trustworthy technologies to ensure user’s safe communications and trustworthy interactions, the SIoT will not reach enough popularity to be considered as a well-established technology. Accordingly, trust management becomes a major challenge to ensure reliable data analysis, qualified services and enhanced security. It helps people exceed their fears and promotes their acceptance and consumption on IoT services. However, current research still lacks a comprehensive study on trust management in SIoT. In this paper, we expose basic concepts, properties and models proposed for the trust management in SIOT environments. Furthermore, we discuss unsolved issues and future research trends.