More than 1,600 people, including survivors of the Holocaust, went to a national ceremony in Liverpool to mark Holocaust Memorial Day.
Six million Jews and millions of other people in groups including Gypsies, homosexuals and disabled people were killed by the Nazis in World War Two.
At the service, faith leaders called for the global end of genocide.
Genocide is where someone is killed because of their race, faith, beliefs or because they belong to a group.
More than 2,000 schools across the UK were also expected to mark the day in some way.
The service marked the 61st anniversary since the liberation of the Auschwitz-Birkenau concentration camp.
Among the speakers were Kay Fyne, whose parents were killed in a Nazi death camp and was herself was on the last train to safety in Britain, and the Rev Leslie Hardman, who took part in the liberation of the Bergen-Belsen concentration and led the first Jewish service there.
There was also a video-message from Prime Minister Gordon Brown in which he urged people to "never forget" the Holocaust.