Amnesty International, which celebrated its 50th anniversary at the end of May, began when the British barrister Peter Benenson read about two Portuguese students being imprisoned for raising a toast to freedom.
Benenson wrote an article in The Observer calling for people to appeal for an amnesty on the prisoners' behalf. The response led to the creation of a small group of volunteers that has grown into one of the best-known campaigning organisations in the world.
Amnesty is now the largest human rights organisation, with three million members and permanent offices in 80 countries.
The most significant milestone, says Champa Patel, head of activism at Amnesty UK, was its decision in 2001 to broaden its remit from campaigning against civil and political rights abuses to all human rights abuses.
"Human rights abuses are all inter-related," she says. "You can't separate them out."
Amnesty now runs campaigns on issues ranging from the detention of prisoners at Guantanamo Bay to improving maternal health. It involves supporters in campaigns, consisting most famously of writing letters on behalf of victims of human rights abuses, but over the years it has employed a variety of campaigning methods.
It published its first report - on conditions for prisoners in Portugal, South Africa and Romania - in 1965; it held its first awareness week for prisoners of conscience in 1968; and it also built support through a series of celebrity fundraising events, such as The Secret Policeman's Ball, the comedy and music gala that was first staged in 1976.
Although letter-writing remains a regular campaign tactic, these days mail is often sent electronically. Today, Amnesty emails members who have signed up to its 'urgent action network', alerting them to human rights violations and asking them to make complaints. Amnesty's website includes sample letters and tips on phrasing to make the process easier.
The charity's 40,000 Facebook friends and 28,000 Twitter followers have opened up new campaigning possibilities. When 14-year-old Faizan Rafiq Hakeem was arrested this year for throwing stones in the Indian state of Jammu and Kashmir and detained for a month without trial, a bombardment of tweets to the state's chief minister from Amnesty supporters led to his release. "Twitter is a good way of mobilising lots of people in a short space of time to get quick wins," says Patel.
The role of social media for campaigning is likely to increase, but the big question for charities is: in what way? "The interesting thing will be how we combine offline and online," says Patel. "It's about translating that sense of solidarity and community offline."
One thing that has barely changed over half a century is Amnesty's logo, depicting a candle in barbed wire. It was chosen for its simplicity and symbolism in 1963 and redesigned in 2000, but the basic elements remain the same. "They are so much a part of who we are I think it would border on blasphemy to alter them," says Patel.