The GREENS workshop provides a forum for practitioners and academics to share knowledge, ideas, practices and current results related to green and sustainable software engineering. This first workshop was held at ICSE 2012 in Zurich, Switzerland. It featured a keynote talk, twelve research position statements and two breakout sessions that discussed topics that ranged from bringing sustainability and energy efficiency into all software lifecycle stages, to green measures and estimations, practices, notations, and tools to both greening the software engineering process, and greening the resulting Information and Communication Technology systems. This report presents the themes of the workshop, summarizes the results of the discussions held in the breakout sessions, as well as the identified research challenges.