Many models of crowd behavior are based on local interactions between pedestrians, but little is known about the actual mechanisms governing these interactions. In Experiments 1 and 2, a participant walked with three human ‘confederates’ or a virtual crowd of 30, while the heading direction or speed of a subset of neighbors was manipulated. In Experiment 3, real crowds of 16 or 20 walked together in a swarming scenario. We find that pedestrians are unidirectionally coupled to neighbors ahead of them, the influence of multiple neighbors is linearly combined, and their weights decrease with distance.