As well as name-calling, describing his former boss as, among other things, a "conman," a "cheat" and a "racist", Michael Cohen make a number of specific claims about Donald Trump.
Here are some of the key points:
Cohen said he was directed by Trump in 2016 to make a $130,000 payment to adult-film star Stormy Daniels to cover up an extra-marital affair.
That payment could amount to an illegal in-kind contribution by Cohen to the campaign because it exceeded donation limits and was not disclosed in Trump's campaign finance reports, legal experts say.
Trump has denied having sex with Daniels and said the payments to her and another woman who claimed an affair were not illegal.
Cohen provided two cheques as evidence for his claims.
Cohen said he was in Trump's office in July 2016 when Roger Stone, a self-described "dirty trickster" and longtime political adviser to Trump, called the then Republican presidential candidate.
Cohen said Stone told Trump he had been speaking with WikiLeaks founder Julian Assange, who told him there would be a dump of emails within a couple of days that would damage Clinton's campaign.
Trump has previously denied knowing in advance about the release of hacked Democratic National Committee emails during the election.
Cohen said Trump continued efforts to build a skyscaper in Moscow during the height of the election campaign, saying he had previously lied in saying the project had been halted beforehand.
He said Trump's lawyers were aware of his false statement and added that the president had publically lied about the project.
Cohen said he had no evidence Trump had colluded with Russia to gain advantage in the election.