A storage system comprising: a first set of parallel rails or tracks and a second set of parallel rails or tracks extending transverse to the first set in a substantially horizontal plane to form a grid pattern comprising a plurality of grid spaces; a plurality of stacks of containers located beneath the rails, and arranged such that each stack is located within a footprint of a single grid space; and a load handling device arranged to move laterally above the stacks on the rails, wherein the load handling device is for lifting and moving the containers stacked in stacks in the storage system and the load handling device comprises: a lifting device, the lifting device comprising a gripper device, the gripper device being configured to grip a container from above, the load-handling device also comprises: a wheel assembly, the wheel assembly comprising a first set of wheels for engaging with the first set of rails or tracks to guide movement of the device in a first direction and a second set of wheels for engaging with the second set of rails or tracks to guide movement of the device in a second direction, wherein the second direction is transverse to the first direction; and a lifting mechanism, the lifting mechanism being configured to raise and lower the gripper device relative to the container-receiving space, the lifting mechanism being located above a container-receiving space, wherein the lifting device is arranged to lift a single container from a stack into the container-receiving space; characterised in that the load-handling device further comprises: an upper part and a lower part, the upper part housing components such as power components, control components, drive components and/or lifting components, the lower part arranged directly beneath the upper part, and the lower part including the container-receiving space located above the rails for accommodating a container; and wherein the load handling device has a footprint that occupies only a single grid space in the storage system. a first set of parallel rails or tracks and a second set of parallel rails or tracks extending transverse to the first set in a substantially horizontal plane to form a grid pattern comprising a plurality of grid spaces; a plurality of stacks of containers located beneath the rails, and arranged such that each stack is located within a footprint of a single grid space; and a load handling device arranged to move laterally above the stacks on the rails, wherein the load handling device is for lifting and moving the containers stacked in stacks in the storage system and the load handling device comprises: a lifting device, the lifting device comprising a gripper device, the gripper device being configured to grip a container from above, a lifting device, the lifting device comprising a gripper device, the gripper device being configured to grip a container from above, a wheel assembly, the wheel assembly comprising a first set of wheels for engaging with the first set of rails or tracks to guide movement of the device in a first direction and a second set of wheels for engaging with the second set of rails or tracks to guide movement of the device in a second direction, wherein the second direction is transverse to the first direction; and a lifting mechanism, the lifting mechanism being configured to raise and lower the gripper device relative to the container-receiving space, the lifting mechanism being located above a container-receiving space, wherein the lifting device is arranged to lift a single container from a stack into the container-receiving space; an upper part and a lower part, the upper part housing components such as power components, control components, drive components and/or lifting components, the lower part arranged directly beneath the upper part, and the lower part including the container-receiving space located above the rails for accommodating a container; and wherein the load handling device has a footprint that occupies only a single grid space in the storage system.