This document discusses energy usage in information and communications technology (ICT). It notes that as mobile ICT equipment like laptops and phones emerged, energy became an important design consideration. Wireless base stations and routers also consume significant energy as they operate continuously. Worldwide PC sales increased dramatically from the 1990s to 2010s, resulting in a large overall carbon emission from ICT equipment. The document highlights that the energy costs during the lifetime of a standard PC, which consumes around 200W continuously, are often more than the initial purchase costs of the PC itself. This raises issues around reducing the energy consumption and costs of powering ICT systems.