Social Internet of Things (SIoT) is a paradigm unifying IoT with Social Networks such that the member human beings and devices interact with each other. This unification leads to several interesting applications. However, as it is common with any interactive system, the respondents are skeptical about their privacy and leakage of information. In order that SIoT becomes a well-established technology, the privacy of user information and secure interactions need to be looked into. Trust management becomes a major challenge to ensure reliable data analysis, qualified services and enhanced security. In this chapter we present the basic concepts, discuss models proposed so far for trust building in SIoT environments. Related issues and scope for future research are also presented.