Facebook founder Mark Zuckerberg has apologised to EU lawmakers for the company's role in the Cambridge Analytica scandal and for allowing fake news to proliferate on its platform.
Mr Zuckerberg apologised for Facebook's tools being used "for harm".
But his testimony did not please all MEPs at the meeting, some of whom felt he had dodged their questions.
One leading UK politician later said the session at the European Parliament had been a "missed opportunity".
"Unfortunately the format of questioning allowed Mr Zuckerberg to cherry-pick his responses and not respond to each individual point," said Damian Collins, chair of the UK Parliament's Digital Culture Media and Sport Committee.
The format was very different from that of Mr Zuckerberg's testimony to US lawmakers in April.
While the US politicians took turns to cross-examine the Facebook chief in a series of back-and-forth exchanges, the leaders of the European Parliament's various political groups each asked several questions apiece.
The tech chief had to wait until they were all delivered before responding.
Mr Zuckerberg spent 22 minutes going through the huge number of questions put to him during the session and was able to pick and choose which to give answers to.
Several of the politicians expressed frustration at this, and one accused Mr Zuckerberg of having "asked for this format for a reason".
A spokesman for Facebook later contacted the BBC to say it had not chosen the structure. This was subsequently confirmed by the parliament's president, Antonio Tajani.
In a follow-up press conference, Mr Tajani added that the MEPs had been aware Mr Zuckerberg's time was limited yet had decided to use up much of the allotted period speaking themselves.
He also drew attention to the fact that the chief executive had agreed to provide follow-up written answers.