Performance limitations of electron‐positron circular colliders are reviewed with emphasis on examining beam‐beam limits through experimental data collected from operating storage rings. Particular emphasis has been put on reviewing scaling laws for the beam‐beam parameter, or ‘‘tune‐shift.’’Observational data on colliders with asymmetric energy are not readily available. Several measurements of the dependence of luminosity and beam‐beam parameter on operating energy are presented to stimulate interest in further experiments.