National Green Week is an annual campaign, started by the Green Education Foundation (GEF), that kicks off during the first week in February and lasts through the end of April. Schools and groups are encouraged to take this opportunity to spend time with students discussing sustainability topics and exploring ways they can make a difference. Participants select one of GEF's six sustainability themes to be their Green Week theme. Each program includes free lessons, activities, audits and contests. Free sustainability themed programs include I Ride Green, Green Energy Challenge, Green Thumb Challenge, Sustainable Water Challenge, Waste Reduction Challenge and the Green Building Program. In 2013, National Green Week is sponsored by the Sprint Foundation.