From their website:
This December, Amnesty supporters across the globe will write millions of letters for people whose basic human rights are being attacked.
It’s all part of Write for Rights, our global letter-writing marathon. It’s one of the world’s biggest human rights events and carries on a long tradition of people like you writing letters to right some of the world’s biggest wrongs.
And it’s not just letters – it could be petitions, emails, Tweets, Facebook posts, photos, postcards… Whatever you think will have the biggest impact, and help bring about change.