The current business model for language education is the student pays — in particular, the student pays Rosetta Stone $500. The problem with this business model is that 95 percent of the world’s population doesn’t have $500.

[Captchas] are not only annoying, but they kill 10 seconds of your time.

People are good at figuring out what's attractive, and computers are good at quickly searching and finding. You put them together, and bang!

The current business model for language education is the student pays — in particular, the student pays Rosetta Stone $500. The problem with this business model is that 95 percent of the world’s population doesn’t have $500.

Before the Internet, coordinating more than 100,000 people, let alone paying them, was essentially impossible. But now with the Internet, I've just shown you a project where we've gotten 750 million people to help us digitize human knowledge.

One fact we're particularly proud of is that there are more people learning languages on Duolingo in the US than there are people learning languages in the entire US public school system.

Together with my advisor, Manuel Blum, I co-invented CAPTCHAs, or computer-generated tests that humans are routinely able to pass but that computers have not mastered (they are the squiggly computer letters that are prevalent across the web).