What is Holocaust Memorial Day?
The Holocaust was one of the most unimaginable crimes in human history, resulting in the deaths of an estimated six million Jewish people.
Its roots lie in anti-Semitism, a hatred for the Jewish community, something Adolf Hitler and his Nazi Party used to galvanise a disillusioned German people in the aftermath of the First World War.
By the start of the Second World War in 1939, Hitler had already deprived the Jewish community of basic civil rights but from this point their persecution became worse. They were crowded into ghettos in their home towns and cities.
By 1942, the Nazis had planned something called 'the Final Solution'. This would see Jewish people gassed in large numbers at concentration camps. It was a deliberately planned act of genocide, an attempt to eradicate an entire race of people. Half a million Roma gypsies were also killed in the Holocaust, as were quarter of a million people with mental and physical disabilities. The Nazis also sterilised deaf people and had members of the gay community imprisoned.
On January 27, 1945, the most infamous concentration camp of them all, Auschwitz in south-west Poland, was liberated by Russian troops.
January 27 is now the day the world remembers the Holocaust, its victims and those of other attempted acts of genocide throughout history.
If you want to learn more about the history behind the Holocaust, this Bitesize guide explains what happened in more detail.
Anne Frank's diary is a well-known account of this period in history. You can find out more about her in this Newsround story.
For further information about Holocaust Memorial Day, visit their website.