German chancellor Angela Merkel was among those paying tributes to the victims of the July 22 shooting in Munich which saw nine people killed.
Ms Merkel joined President Joachim Gauck at a non-denominational church service at the Frauenkirche, or Church of Our Lady - the first of two memorial events.
Mr Gauck was speaking later in the day at an event in Bavaria's state parliament.
An 18-year-old German-Iranian man killed nine people and wounded over 30 others at a McDonald's restaurant and shopping mall in the city. He then killed himself.
The gunman was a withdrawn loner obsessed with playing "killer" video games who had been treated for depression and psychiatric problems, said officials.
Witnesses have said the gunman shouted slurs against foreigners, even though he himself was the German-born son of Iranian asylum-seekers
The restaurant where most of the victims died was a hangout for youths of immigrant backgrounds, and the dead included victims with Hungarian, Turkish, Greek, and Kosovo Albanian backgrounds and a stateless person.
There is no suggestion that Islamic extremism played any part in the Munich attack.
However, the rampage in Munich was the deadliest of a string of attacks over a week that shook Germany.
They included an axe attack and a bombing in Bavaria that were both claimed by the Islamic State group.