An object handling system comprising: two substantially perpendicular sets of rails (22, 22b) defining a grid, the grid comprising a plurality of grid spaces; a series of uprights, the uprights supporting a first set of parallel horizontal members and a second set of parallel horizontal members, the first set of members being arranged perpendicularly to the second set of members to form a plurality of horizontal grid structures supported by the uprights, the uprights, the horizontal members (18, 20) and the rails together defining a framework; a plurality of containers arranged in stacks, located beneath the grid members (18, 20) and between uprights, within the framework, wherein the containers are stacked between the members (16, 18, 20) of the framework, so that the framework guards against horizontal movement of the stacks, and guides vertical movement of the containers, the stacks of containers defining a workspace, the object handling system further comprising a plurality of robotic load handling devices positioned above the framework 14 and operating on the rails above the workspace, the load handling devices comprising a body mounted on wheels (34, 36), a first set of wheels being arranged to engage with at least two rails of the first set of rails, the second set of wheels being arranged to engage with at least two rails of the second set of rails, the first set of wheels being independently moveable and driveable with respect to the second set of wheels such that when in motion only one set of wheels (34, 36) is engaged with the rails forming the grid at any one time thereby enabling movement of the load handling devices along the rails to any point on the grid by driving only the set of wheels (34, 36) engaged with the rails, the load handling devices further comprising means for removing or replacing containers from the stacks; wherein a portion of the stacks are independently movable with respect to the remaining stacks in the workspace, and are removable from or replaceable in to the workspace by mechanical moving means, characterised in that the mechanical moving means comprises a roll cage mounted on wheels manoeuvrable in to and out of position within the workspace by manual or robotic means. two substantially perpendicular sets of rails (22, 22b) defining a grid, the grid comprising a plurality of grid spaces; a series of uprights, the uprights supporting a first set of parallel horizontal members and a second set of parallel horizontal members, the first set of members being arranged perpendicularly to the second set of members to form a plurality of horizontal grid structures supported by the uprights, the uprights, the horizontal members (18, 20) and the rails together defining a framework; a plurality of containers arranged in stacks, located beneath the grid members (18, 20) and between uprights, within the framework, wherein the containers are stacked between the members (16, 18, 20) of the framework, so that the framework guards against horizontal movement of the stacks, and guides vertical movement of the containers, the stacks of containers defining a workspace, the object handling system further comprising a plurality of robotic load handling devices positioned above the framework 14 and operating on the rails above the workspace, the load handling devices comprising a body mounted on wheels (34, 36), a first set of wheels being arranged to engage with at least two rails of the first set of rails, the second set of wheels being arranged to engage with at least two rails of the second set of rails, the first set of wheels being independently moveable and driveable with respect to the second set of wheels such that when in motion only one set of wheels (34, 36) is engaged with the rails forming the grid at any one time thereby enabling movement of the load handling devices along the rails to any point on the grid by driving only the set of wheels (34, 36) engaged with the rails, the load handling devices further comprising means for removing or replacing containers from the stacks; wherein a portion of the stacks are independently movable with respect to the remaining stacks in the workspace, and are removable from or replaceable in to the workspace by mechanical moving means, characterised in that the mechanical moving means comprises a roll cage mounted on wheels manoeuvrable in to and out of position within the workspace by manual or robotic means.