Travis Kalanick took to the stand in San Francisco - where two of the biggest firms in the sphere of self-driving technology are going head-to-head - and he was questioned about allegations that he arranged the theft of trade secrets from Waymo.
Mr Kalanick is alleged to have staged a meeting with former Google employee Anthony Levandowksi to discuss the issue.
During the trial, the jury was shown an Uber visitor pass and notes that were supposedly taken in the meeting.
The notes featured the phrase, "laser is the sauce", which is said to be a reference to the technology at the centre of the trial.
Alphabet lawyer Charles Veerhoven said in his opening statement: "Mr Kalanick, the chief executive officer at the time at Uber, made a decision that winning was more important than obeying the law."
Alphabet alleges that 14,000 files of data were downloaded that could be used to develop driverless car technology.
Mr Kalanick - who has insisted he does not recall the meeting - resigned as chief executive of Uber during the summer, amid pressure from shareholders.
However, he is still on Uber's board.
Mr Levandowksi founded Otto, which was subsequently acquired by Uber, following his departure from Google.
Uber, for its part, doesn't dispute that the documents were taken.
But the American firm has claimed it hasn't benefited from them.