The former deputy prime minister was shot dead shortly before he was due to lead a protest against Mr Putin's rule
Russians are marking one year since opposition politician Boris Nemtsov was gunned down just metres from the Kremlin.
People have laid flowers and candles at the scene of his murder and a memorial march is planned through Moscow, with other commemorative events scheduled across the country and abroad.
Mr Nemtsov, a fierce critic of Russian President Vladimir Putin, was shot four times in the back just a day-and-a-half before he was due to lead a protest against Mr Putin's rule.
The 55-year-old, a former deputy prime minister in Boris Yeltsin's government, had been walking across the Moskvoretsky Bridge with his Ukrainian model girlfriend when he was killed.
Among those paying respect was US ambassador John Tefft, who laid a wreath with a ribbon saying: "From the American people."
He said he had come to "honour the memory of a man who we knew as a government official, as a politician and, for many Americans, as a friend".
He added: "We are here today to honour his memory, the values for which he stood and to express our hope for the future that some of the dreams that Boris Nemtsov had will come true in Russia."
The commemorations have not been without controversy however.
Dmitry Gudkov, one of the few independent voices in the Russian parliament's lower house, said the suggestion of a moment of silence in Mr Nemtsov's memory was refused by most other deputies.
While the march has been allowed to go ahead, people have been forbidden from marching to the bridge where Mr Nemtsov's supporters have tried to maintain a shrine to him.
Five Chechens are awaiting trial for what prosecutors say was a contract killing planned over many months.
But Mr Nemtsov's family blame Chechnya's Moscow-backed strongman Ramzan Kadyrov and the Kremlin itself, saying authorities have failed to bring the masterminds of the killing to justice.