To address a wide range of multi-robot coordinated movement tasks we seek a formation strategy that offers: scalability: the approach should easily scale to any number of agents, locality: the behaviors should depend only on the local sensors of each agent, flexibility: the behaviors should be flexible to support many formation shapes.To provide these features we introduce a new behavior-based approach to robot formation keeping. The new strategy is based loosely on the way molecules form crystals. From the point of view of each robot in the group, every other robot has several local “attachment sites” other robots may be attracted to. This type of attachment site geometry roughly corresponds to molecular covalent bonding. Just as different crystal shapes result from different covalent bond geometries, robot formation shapes are influenced by the attachment site geometries employed.