The Internet of Behavior is a research theme that aims to analyze human behavior data on the Internet from the perspective of behavioral psychology, obtain insights about human behavior, and better understand the intention behind the behavior. In this way, the Internet of Behavior can predict human behavioral trends in the future and even change human behavior, which can provide more convenience for human life. With the increasing prosperity of the Internet of Things, more and more behavior-related data is collected on the Internet by connected devices such as sensors. People and behavior are connected through the extension of the Internet of Things -- the Internet of Behavior. At present, the Internet of Behavior has gradually been applied to our lives, but it is still in its early stages, and many opportunities and challenges are emerging. This paper provides an in-depth overview of the fundamental aspects of the Internet of Behavior: (1) We introduce the development process and research status of the Internet of Behavior from the perspective of the Internet of Things. (2) We propose the characteristics of the Internet of Behavior and define its development direction in terms of three aspects: real-time, autonomy, and reliability. (3) We provide a comprehensive summary of the current applications of the Internet of Behavior, including specific discussions in five scenarios that give an overview of the application status of the Internet of Behavior. (4) We discuss the challenges of the Internet of Behavior's development and its future directions, which hopefully will bring some progress to the Internet of Behavior. To the best of our knowledge, this is the first survey paper on the Internet of Behavior. We hope that this in-depth review can provide some useful directions for more productive research in related fields.