Reinhold Hanning faces court in the western town of Detmold seven decades after the defeat of the Nazis, charged with at least 170,000 counts of being an accessory to murder in his role at the camp in occupied Poland.
The trial is the first of three scheduled this year against former SS men, as Germany races to prosecute ageing Third Reich criminals.
Christoph Heubner, vice president of the International Auschwitz Committee, said it was an opportunity to make up "for the failures of Germany's justice system".
Holocaust survivor Angela Orosz, who will testify against Hanning, told AFP that all Auschwitz staff "were part of this killing machine".
"Without these people and their active support for the Holocaust, what happened in Auschwitz, the murder of 1.1 million people in just a few years, would not have been possible, and perhaps many of my family members would still be alive," said Orosz, who was born in Auschwitz just over a month before it was liberated on January 27, 1945.
After the charge sheet is read out Thursday against Hanning, the court will hear from three German plaintiffs -- Holocaust survivors Leon Schwarzbaum, Erna de Vries and Justin Sonder.
Sonder, 90, said that "this trial should have been held 40 or 50 years ago".
But "even today, it is not too late to look at what happened", said Sonder, who lost 22 members of his family under the Nazi regime and was sent to Auschwitz when he was 17 years old.
Ronald Lauder, president of the World Jewish Congress, agreed.
"Even 71 years after the liberation of Auschwitz, the wounds of the survivors are still fresh. Many of them are haunted every single day by the horrible experiences they and their family members went through," he told AFP.
"As long as it's possible to bring any of them to justice, it must be done," he said.
