We warmly welcome you to the 2015 IEEE Online Conference on Green Communications (OnlineGreenComm), the fifth edition conducted entirely online and dedicated to addressing the challenges in energy-efficient communications and communications for green technologies. Continuing with the experience provided by the last four editions, IEEE OnlineGreenComm'15 will be held virtually, to emphasize the need for reducing global greenhouse gas emissions, avoiding the most polluting aspects of conferences - the use of mass transport systems for traveling. Common to all IEEE conferences, IEEE OnlineGreenComm will feature a full-fledged paper submission, review, and publication process that adheres to the high standards defined by IEEE. IEEE OnlineGreenComm covers a wide spectrum of research subjects, including green methodologies and architectures for communication technologies, communication technologies as enablers for green solutions, energy efficiency in Smart Grid communications, and energy management.