The document summarizes a Green Hackathon event held in Athens from December 14-16, 2012. Over 60 registered hackers and 40 non-hackers participated in a 2.5 day event across 3 venues: a kick-off session to brainstorm ideas, a 24-hour hacking marathon, and a final presentation event where the top 4 winning hacks were announced. The 2013 hackathon was scheduled for November 8-9 and aimed to create a small green hacking community in Athens and provide collaboration experience for groups working on environmental projects.