Holocaust Memorial Day will today commemorate victims of Nazi persecution and subsequent genocides in Cambodia, Rwanda, Bosnia and Darfur.
Services, lectures, discussions and screenings will take place in Britain and around the world to remember those whose lives were destroyed during the Holocaust.
The Archbishop of Canterbury has used a video message to mark the day to urge people to speak out on behalf of communities, neighbours and strangers alike.
In line with the Speak Up, Speak Out theme of today’s event, Dr Rowan Williams encouraged people to challenge themselves: "Who do we speak for? Are we willing to speak for the neighbour and for the stranger, for people like us and also people who are not like us?"
Reflecting on the atrocities of the Holocaust, Dr Williams remarked that "one of the things that prevents it just being a totally dark night is the presence of some of those who were willing to speak for strangers and to take risks alongside strangers".
This year's memorial day focuses on encouraging people to use their voice to speak out against injustice, humiliation and hatred and Dr Williams emphasises his own belief that such speech is "profoundly and eternally worthwhile".
The Archbishop draws parallels between events of the 1930s and '40s and continuing problems in the developing world.
Describing a visit he made to Congo last year, he said: "I heard there something of the experience of people who have lived through genocide of another kind - people who didn't know and couldn't rely on the fact that there were others to speak for them."
But he said there were "signs of hope".
In his video message, Dr Williams also commented on the recent 70th anniversary of the foundation of the Council of Christians and Jews, which he says resulted in "decades of intense friendship and relationship building" which he hopes "will be part of what we take forward into the next generation".
He cites one of the founders of the Council, Archbishop William Temple, who had "come to the conclusion that he had to learn to speak for the stranger", and in 1943 had argued in the House of Lords that the West had to do more to combat the atrocities against Jews under the Nazi regime.
Members of the public in London are also being urged to sign a pledge to challenge the language of hatred.
A pledge signing is taking place in Trafalgar Square between 9am and 7pm on Thursday giving people the chance to sign the Holocaust Memorial Day Trust's newly created pledge pillars and commit to speak up against discrimination and persecution wherever they see it.
James Hurst, acting director of the Holocaust Memorial Day Trust, said: "Support for Holocaust Memorial Day has grown enormously, with a 350% increase since 2005 in activities which take place on or around the day.
"The Trafalgar Square pledge signing is a fantastic opportunity for members of the public to commit to ending discrimination and persecution in their communities."
Read Mary Creagh’s blog An International Response to Prevent Future Genocides