What's it all about?
President Trump's campaign and transition teams have been accused of colluding with Russian agents to influence the US election in the Republican candidate's favour.
US intelligence agencies, including the CIA and NSA [National Security Agency], concluded with "high confidence" in 2016 that Russia was behind an effort to thumb the scale of the US election for Mr Trump.
Both the Russian and US presidents have poured scorn on suggestions of collusion, with Mr Trump calling it "the greatest political witch hunt in history".
What contact do we know about?
At least 12 Trump associates had contacts with Russians during the campaign or transition, according to an analysis of public records by CNN, with at least 19 face-to-face interactions with Russians or Kremlin-linked figures and at least 51 individual communications.
Trump aides known to have had contact with Russians include the president's son-in-law and adviser Jared Kushner, his son Donald Trump Jr, former National Security Adviser Michael Flynn, and the Attorney General Jeff Sessions.
The president's supporters point out that interactions with foreign nationals are routine during any White House campaign, but two Trump aides have admitted lying about the encounters.
Who's been charged?
Four people have been indicted by the special counsel: Paul Manafort, a former Trump campaign chairman; Rick Gates, a former business associate of Mr Manafort; George Papadopoulos, a former Trump campaign adviser, and Michael Flynn, the former US national security adviser.
Mr Manafort and Mr Gates have pleaded not guilty to 12 counts including money laundering and conspiracy against the US. The indictments do not mention Mr Trump or alleged Russian interference in the election.
Mr Papadopoulos is said to have attempted to set up meetings between Mr Trump and Russian representatives, and he admitted lying to the FBI about his contacts with Russians. Mr Flynn pleaded guilty to lying to the FBI over meetings he had with the Russian Ambassador, Sergei Kislyak.
Why are the Flynn charges important?
By far the most senior member of the Trump team to be indicted, Michael Flynn, admitted one count of making false statements. This was a much lesser charge than analysts say he might have faced for conducting business as a private citizen with a foreign power. Legal experts say such plea deals are only offered when a witness has incriminating evidence on someone more senior than themselves.
Mr Trump sacked Mr Flynn in February, saying he had lied to Vice-President Mike Pence about meeting with the Russian envoy to the US. Questions have been raised over how much Mr Trump knew about Mr Flynn's contacts with the Russian ambassador and when. The answers to those questions could form part of Mr Flynn's plea bargain, US media say.
How many investigations are ongoing?
As well the special counsel inquiry by Robert Mueller under the aegis of the Justice Department there are four congressional investigations:
- The Senate and House Intelligence Committees and the Senate Judiciary Committee are investigating alleged Kremlin meddling and any collusion with Trump aides
- The House Oversight Committee is scrutinising links between Trump associates and Russian officials
All you need to know about Trump Russia story