All market and technology studies forecast an explosive growth in the number of "things" that will be connected to the Internet. The resulting network is what is commonly known as the "Internet of Things" (IoT). When compared to the traditional Internet, the extremely high complexity of the IoT environments (usually characterized by a huge number of nodes, high heterogeneity of their resources and capabilities, uncertainty on their trustworthiness, etc.) poses new challenges that cannot be faced by even very smart objects singularly.Social behavior is the answer found by several creatures to face the complexity of the surrounding environment. Accordingly, the concept of Social Internet of Things (SIoT) has been recently introduced and is the subject of a rapidly increasing research effort.During the tutorial the introduction of social notions into the IoT will be motivated, the basic concepts of the SIoT paradigm explained, and the existing related research results and industrial experimentations surveyed. Besides, the architecture of a sample SIoT-based platform will be detailed together with some exemplary applications. Reference web site for this tutorial: http://www.social-iot.org