The Internet of Things (IoT) is seen as a novel technical paradigm aimed at enabling connectivity between billions of interconnected devices all around the world. This IoT is being served in various domains, such as smart healthcare, traffic surveillance, smart homes, smart cities, and various industries. IoT's main functionality includes sensing the surrounding environment, collecting data from the surrounding, and transmitting those data to the remote data centers or the cloud. This sharing of vast volumes of data between billions of IoT devices generates a large energy demand and increases energy wastage in the form of heat. The Green IoT envisages reducing the energy consumption of IoT devices and keeping the environment safe and clean. Inspired by achieving a sustainable next-generation IoT ecosystem and guiding us toward making a healthy green planet, we first offer an overview of Green IoT (GIoT), and then the challenges and the future directions regarding the GIoT are presented in our study.