Technology is changing the way we live and the way we interact with the world. We are witnessing advancements in several fields, from Internet services to quantum computing, personal assistants, or even artificial intelligence. Internet of Things devices that surround us also increase in number every day. Furthermore, these devices have increasing capabilities, with more processing power, faster and more reliable communication mechanisms, and more sensors to interact with the physical world. Internet of Things devices also allow us to create “smarter” systems. However, no matter how many devices and sensors make up a system, and truly smart environments can only be developed by integrating humans into the overall system. Human actions, emotions, intents, and desires can largely affect the way systems behave and perform, and they are able to either improve a system or make it perform worse. As such, we must design our systems with the human factor in mind, not only as an end-user but, above all, as a fully integrated “component” of the system. We now have at our disposal new means to perceive humans and better integrate them into emerging systems like the Internet. Most humans now carry, at all times, smartphones that have several sensors, able to communicate with other devices and services, and even have the necessary processing power to make inferences about human states. At the same time, with the proliferation of social networks, humans themselves can act as sensors (i.e., social sensors). Advances in radiofrequency and image processing are also making possible the development of new unobtrusive sensing technologies that can be used to gather information on human activity and states, without the need for any human action. Additionally, we now have interactive agents/chatbots that allow for human-like interaction of systems with humans. In this chapter, we target all the aforementioned technology advancements. As a starting point, we review relevant Internet technologies and we identify, analyse, and discuss state-of-the-art solutions for the Human-in-the-Loop Cyber-Physical Systems paradigm. We then present a novel model for this paradigm that considers humans in all phases of the cyber-physical loop.