Information cascades (Bikhchandani-Hirshleifer-Welch 1992) occur when rational Bayesian agents ignore private signals and follow the crowd. Each agent sees all prior actions and receives a private signal (correct with probability q). Once the action history is sufficiently lopsided, it overwhelms any private signal — a cascade begins. Cascades can be wrong (herding on the incorrect option) if early agents were unlucky.