The Internet of Things (IoT) has become one of the unprecedented research trends for both academic and commercial organizations. Every day, the publicity of the IoT is increased. This is because the unlimited benefits that the IoT can bring to our environment. The IoT has the ability to connect almost all objects of real-world to communicate and cooperate with each other over the Internet to facilitate generating new applications and services that can improve our quality of life. This paper provides an overview of the IoT system with highlighting its applications, challenges, and open issues. It starts with discussing the state-of-the-art of the IoT system and its layered architecture. This is followed by discussing different characteristics of the IoT with presenting a comparison between common IoT communication technologies. Different IoT applications and challenges are also discussed. At the end, open research directions related to the IoT are also presented.