In this chapter, we discuss the root of social intelligence from the perspective of human intelligence (HI), artificial intelligence (AI), and their integration. The interdisciplinary nature of social intelligence is also highlighted with a detailed discussion on closely related domains, such as natural language processing and text mining, computer vision and image processing, social computing and human-computer interaction, estimation theory, and statistical learning. Additionally, we present a few emerging social intelligence applications in real-world scenarios to further demonstrate the necessity of this new intelligence paradigm. Examples of these applications include social media misbehavior identification and mitigation, multimodal truth discovery, explainable AI and machine learning, disaster response and damage assessment, AI and crowdsourcing for education, and social sensing in smart city applications.