A sequencing system and a robotic storage and picking system include a plurality of containers disposed in stacks beneath a grid having a first set of tracks and second set of tracks, the first and second sets of tracks being disposed substantially perpendicular to each other. Plural load handling devices are operable on the grid, the load handling devices lifting and depositing containers from and to the stacks. The load handling devices can deposit containers on to conveyor belts into predetermined positions, the positions being fillable in any random order and multiple positions being fillable at any one time.