A federal indictment charged 13 Russians in a plot to interfere in the 2016 US presidential election.
The indictment also targets a Russian Internet agency.
Here are some of the key facts and players in Special Counsel Robert Mueller's 37-page indictment
:: Putin's chef
One of the key figures in the indictment is a Russian restaurateur believed to have ties to Vladimir Putin.
Yevgeny Prigozhin has earned his nickname because his restaurants and catering businesses have hosted the Russian President's dinners with foreign dignitaries.
He is an entrepreneur from St Petersburg who established relationship with Mr Putin about 10 years ago.
He has dismissed the indictment. "Americans are very impressionable people," he told Russian state news agency RIA Novosti. "They see what they want to see."
:: Troll factory
According to the indictment, the Russian Internet Research Agency sought to conduct "what it called 'information warfare against the United States of America' through fictitious US personas on social media platforms and other internet-based media".
Based in St. Petersburg, Mr Putin's hometown, the Russian Internet Research Agency employs bloggers and online commentators to try to influence public opinion in Russia and abroad.
According to the indictment, the company was funded by Mr Prigozhin and purchased internet advertisements in the names of Americans whose identities they had stolen. It also allegedly staged political rallies while posing as American political activists and paid people in the US to promote or disparage candidates.
:: Robert Mueller
The chief of the investigation, Robert Mueller has a long history in the intelligence community. He was appointed FBI director shortly before the Sept 11 attacks and stayed on in the position for the 12 years, transforming the bureau into a national intelligence agency.
Mr Mueller retired from government in 2013 and joined a private law firm. He was appointed special counsel in May 2017 by Deputy Attorney General Rod Rosenstein.
His investigation is continuing.
:: Trump's reaction
Donald Trump says the indictments vindicate him as they show there was no collusion between Russians and his campaign.
Russia started their anti-US campaign in 2014, long before I announced that I would run for President. The results of the election were not impacted. The Trump campaign did nothing wrong – no collusion!
— Donald J. Trump (@realDonaldTrump) February 16, 2018
A White House statement said the President was "glad to see the Special Counsel's investigation further indicates – that there was NO COLLUSION between the Trump campaign and Russia and that the outcome of the election was not changed or affected".
"It's time we stop the outlandish partisan attacks, wild and false allegations, and far-fetched theories, which only serve to further the agendas of bad actors, like Russia, and do nothing to protect the principles of our institutions," Mr Trump said in the statement.
The indictments do not mention collusion at all.
:: 'Unwitting individuals'
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According to the indictment, some officials in Mr Trump's campaign helped the Russian meddling – but unknowingly, the document stresses.
Some of the Russians indicated in the indictment posed as Americans and communicated with "unwitting individuals" associated with Mr Trump's election team in order to coordinate activities, the team says. Sometimes the Russians used fake US personas in order to communicate with officials in Mr Trump's team.