A material handling system for storing or retrieving a plurality of items, comprising: a plurality of vehicles for delivering and retrieving items, wherein each vehicle comprises an on-board motor for driving the vehicle; a first rack of storage locations; a second rack of storage locations spaced apart from the first rack; a plurality of storage containers wherein each storage location is configured to receive a plurality of the storage containers; an aisle located between the first and second racks, wherein the vehicles are displaceable vertically and horizontally within the aisle, wherein the system comprises a track for guiding the vehicles, wherein the track comprises: a plurality of horizontal track sections (135, 140) spaced apart from one another and extending in a generally horizontal direction; a plurality of vertical track sections spaced apart from one another and extending in a generally vertical direction, wherein the vertical track sections intersect the horizontal track sections to form a loop; and an intersection where one of the horizontal track sections intersects one of the vertical track sections, wherein the intersection provides a first path in a generally horizontal direction and a second path in a generally vertical direction, the material handling system being characterized in that a first of the storage containers comprises a first connector at a first end and a second of the storage containers comprises a second connector at a second end, wherein the first connector is releasably connectable with the second connector to releasably connect the first and second storage containers at one of the storage locations; and in that each vehicle comprises a transfer mechanism for transferring the first and second storage containers between the vehicle and the one storage locations wherein the releasable connection between the first and second containers is operable to displace the second storage container when the transfer mechanism displaces the first storage container. a plurality of vehicles for delivering and retrieving items, wherein each vehicle comprises an on-board motor for driving the vehicle; a first rack of storage locations; a second rack of storage locations spaced apart from the first rack; a plurality of storage containers wherein each storage location is configured to receive a plurality of the storage containers; an aisle located between the first and second racks, wherein the vehicles are displaceable vertically and horizontally within the aisle, wherein the system comprises a track for guiding the vehicles, wherein the track comprises: a plurality of horizontal track sections (135, 140) spaced apart from one another and extending in a generally horizontal direction; a plurality of vertical track sections spaced apart from one another and extending in a generally vertical direction, wherein the vertical track sections intersect the horizontal track sections to form a loop; and an intersection where one of the horizontal track sections intersects one of the vertical track sections, wherein the intersection provides a first path in a generally horizontal direction and a second path in a generally vertical direction, the material handling system being characterized in that a first of the storage containers comprises a first connector at a first end and a second of the storage containers comprises a second connector at a second end, wherein the first connector is releasably connectable with the second connector to releasably connect the first and second storage containers at one of the storage locations; and in that each vehicle comprises a transfer mechanism for transferring the first and second storage containers between the vehicle and the one storage locations wherein the releasable connection between the first and second containers is operable to displace the second storage container when the transfer mechanism displaces the first storage container. a plurality of horizontal track sections (135, 140) spaced apart from one another and extending in a generally horizontal direction; a plurality of vertical track sections spaced apart from one another and extending in a generally vertical direction, wherein the vertical track sections intersect the horizontal track sections to form a loop; and an intersection where one of the horizontal track sections intersects one of the vertical track sections, wherein the intersection provides a first path in a generally horizontal direction and a second path in a generally vertical direction, the material handling system being characterized in that a first of the storage containers comprises a first connector at a first end and a second of the storage containers comprises a second connector at a second end, wherein the first connector is releasably connectable with the second connector to releasably connect the first and second storage containers at one of the storage locations; and in that each vehicle comprises a transfer mechanism for transferring the first and second storage containers between the vehicle and the one storage locations wherein the releasable connection between the first and second containers is operable to displace the second storage container when the transfer mechanism displaces the first storage container.