We have had a lot of these controls in place for years. Here's how he opened this morning.
As for the federal Russian Federation probe that has occupied much of Washington's attention for months, he said he had not been interviewed by special counsel Mueller's team, but "I know we're working with them". "It was my mistake and I'm sorry", Zuckerberg said on Tuesday.
Zuckerberg described Facebook as an "idealistic and optimistic company" which focuses on the positive aspect of connecting people.
John Thune of South Dakota said Zuckerberg's company had a 14-year history of apologizing for "ill-advised decisions" related to user privacy.
Back in the United Kingdom, the secretary of state for digital, culture, media and sport Matt Hancock today met with senior Facebook executives to discuss "data issues". In fact, it may be the only truly valuable thing about Facebook.
The simplest explanation for this is that Facebook uses that data to make money.
Some lawmakers grew frustrated at their limit of four minutes each to press Mr. Zuckerberg on specifics, and chastised the billionaire at times for offering up rehearsed platitudes about valuing user privacy.
"The only way we're going to close this trust gap is through legislation that creates and empowers a sufficiently resourced expert oversight agency, with rulemaking authority to protect the digital privacy and ensure that companies protect our users' data". It's a broad system.
"With all due respect, Facebook is actually enabling an illegal activity and, in so doing, you are hurting people". "We do not allow hate groups on Facebook overall", he added. Lindsey Graham about whether Facebook is a monopoly, and today has also (so far) produced one good round of questions.
On the topic of Russian meddling in the 2016 USA election, Mr Zuckerberg admitted it would be hard to completely eradicate such behaviour for "as long as Russia employs people for the activity".
During Wednesday's hearing, Zuckerberg divulged that his own personal data had been sold to a third party.
SELYUKH: So this is the first time.
Representative Anna Eshoo, reading questions from her constituents in and around Silicon Valley, California, asked Mr Zuckerberg whether he was one of the 87 million people whose data may have been handed to the controversial firm. The app vacuumed up not just the data of the people who took it, but also - thanks to Facebook's loose restrictions - data from their friends, too, including details that they hadn't meant to share publicly. The company said it will be alerting any affected users about any abuses discovered during the audit.
KING: OK, so some new insights here today - what do we expect to come out of these hearings in the end?