Abstract: An order fulfillment system includes a plurality of stock locations for storing items, and movable collection containers, each configured to hold one or more of the items. A network of tracks along which each of the collection containers is configured to move in a single direction includes junctions where at least two of the tracks intersect, each collection container being controllable at a junction to continue travelling along one of the tracks. The network of tracks is configured to enable the collection containers to move to the stock locations. A controller is configured to receive a list of ordered items, to determine a selected stock location at which each ordered item is stored, to calculate a route along the network of tracks to bring a collection container to each selected stock location, and to control movement of that collection container along the calculated route to the selected stock locations.