The launch upends its founders’ original mission of creating an app with ‘No Ads! No Games! No Gimmicks!’ This week, WhatsApp did something its founders said it would never do: it’s putting advertisements inside the app. It ends WhatsApp’s decade-plus run of offering an ad-free messaging and calling experience.

I talked with a professor of advertising to make sense of what this means for all of us who use those social media platforms.

WhatsApp says that users will start seeing ads in parts of the app, as owner Meta Platforms moves to cultivate a new revenue stream by tapping the billions of people that use the messaging service.