It's the first time before Congress for the founder and CEO and comes amid a firestorm of user concerns and government probes. The social media giant is facing questions after reports that research firm Cambridge Analytica improperly gained access to the personal information of as many as 87 million Facebook users.
In a prepared testimony released on Monday, Zuckerberg said that Facebook made a "big mistake," adding: "I started Facebook, I run it, and I'm responsible for what happens here." At least some lawmakers have publicly agreed.
Zuckerberg will appear at a joint hearing of the Senate Judiciary and Commerce committees Tuesday and at a hearing of the House Energy and Commerce Committee Wednesday.
After reading his testimony, here are some of the tough questions we'd like answers to: