What happens when a group of people band together? It depends. The organization of a crowd, the tools it uses, and its culture all determine its impact. Is it structured to collaborate or fight? Does each node have ways to connect with and trust the others? Do its members require anonymity or personal space? Here, we explore these dynamics by building up the biggest crowds and how they’re counted, then breaking down what makes them buzz and swarm. And don’t forget that where there are masses, there’s value—and that too can be quantified.