They are the four most powerful men on the virtual planet.
But today for the first time, Mark Zuckerberg of Facebook, Jeff Bezos of Amazon, Tim Cook of Apple and Sundar Pichai of Alphabet, which owns Google, are all appearing in front of the House subcommittee on market dominance.
The main issue – are they using their commanding position to stop other companies getting a foothold in markets across the internet?
Our Washington correspondent Siobhan Kennedy is live in Washington.
Plus, our correspondent Inigo Gilmore reports.
We did ask representatives from all four companies to speak to us but to no avail.