The Internet of Things (IoT) is a technical revolution that represents the future of computing and communications. Under its vision, the next-generation Internet will promote the harmonious interaction between human, society, and smart things. The current research in IoT is mainly from the perspective of connecting and managing things. The humanized, social side of IoT, however, is still not explored. In this article, we intend to present the IoT from the human-centric perspective. By analyzing the tight-coupled relationship between human and opportunistic connection of smart things (e.g., mobile phones, vehicles), we propose Opportunistic IoT. It enables information sharing and dissemination within/among opportunistic communities that are formed with the movement and opportunistic contact nature of human. We characterize the bi-directional effect between human and opportunistic IoT, present the innovative application areas, and discuss the challenges raised by this new computing paradigm.