The next of wireless networks (i.e., 6G) is envisioned to support communication in the three-dimensional space by integrating space, aerial, terrestrial, and undersea networks. The overall goal is to provide ubiquitous and unlimited connectivity to a massive number of Internet of Things (IoT) and machine-type devices/users having diverse Quality of Service (QoS) requirements, supporting substantial and heterogeneous traffic demands, and reducing the energy consumption with the help of highly energy-efficient communication protocols, transceivers and computing technologies. Out of several innovations 6G is targeting, this special issue focuses on green communications and computing technologies, which are crucial to reduce the overall energy consumption and operational cost from both the environmental and business viewpoints. To this end, the ever-increasing demand for advanced and ubiquitous applications over the recent years has shifted the paradigm of self-organizing networks to self-sustainable networks (SSNs). One main goal of SSNs is to eliminate the need for separate charging of heterogeneous devices by combining energy-efficient communication, energy harvesting/power transfer techniques, and offloading of energy-intensive processing from the edge-devices to the edge- and cloud-servers. However, the coexistence of wireless information and power transfer systems/links should be as seamless as possible for the end-users. Furthermore, providing network sustainability, and energy-efficient, energy-aware, and environment-aware connections to the massive number of devices and users having different levels of processing capabilities is one of the key challenges.