A system for transporting inventory, comprising a first level and a second level that is arranged vertically differently from the first level, and further comprising: a plurality of storage shelves, each storage shelf including a frame and a plurality of bin modules that are removably supported in the frame, a collection shelf including a frame configured to removably support multiple bin modules, and a dolly; wherein said plurality of storage shelves, said collection shelf, and said dolly are placed on the second level, and the system still further comprises an elevator placed on the first level and configured to move the multiple bin modules removably supported in said collection shelf between said collection shelf and the first level; wherein each bin module includes a first coupler and a plurality of bins for storing inventory items; wherein said dolly includes: (a) a dolly frame, (b) a first drive module configured to propel the dolly, (c) a first actuator configured to move a second coupler to couple to the first coupler of the bin module removably supported in one of the plurality of storage shelves when the dolly is positioned adjacent to one of said plurality of storage shelves, the first actuator being further configured to remove said bin module from one of said plurality of storage shelves to the dolly frame, and to move said bin module from the dolly frame to the collection shelf when the dolly is positioned adjacent to the collection shelf and to uncouple the second coupler from the first coupler of said bin module; and (d) a first control unit configured to control operation of the first drive module and the first actuator, wherein the second coupler of the dolly comprises one or more arms movable by the first actuator to extend to and retract from said storage shelf when the dolly is positioned adjacent to the said storage shelf; and wherein the elevator includes an elevator frame, a second drive module configured to propel the elevator, the system for transporting inventory being characterised in that: the elevator comprises a second actuator configured to move a third coupler for holding a bin module both vertically and horizontally, and a second control unit that controls operation of the second drive module and the second actuator; wherein said third coupler is configured, as with the second coupler of the dolly, to couple to, and uncouple from, a corresponding coupler of one of the plurality of bin modules; and wherein said third coupler of the elevator is of the form of the second coupler of the dolly. a plurality of storage shelves, each storage shelf including a frame and a plurality of bin modules that are removably supported in the frame, a collection shelf including a frame configured to removably support multiple bin modules, and a dolly; wherein said plurality of storage shelves, said collection shelf, and said dolly are placed on the second level, and the system still further comprises an elevator placed on the first level and configured to move the multiple bin modules removably supported in said collection shelf between said collection shelf and the first level; wherein each bin module includes a first coupler and a plurality of bins for storing inventory items; wherein said dolly includes: (a) a dolly frame, (b) a first drive module configured to propel the dolly, (c) a first actuator configured to move a second coupler to couple to the first coupler of the bin module removably supported in one of the plurality of storage shelves when the dolly is positioned adjacent to one of said plurality of storage shelves, the first actuator being further configured to remove said bin module from one of said plurality of storage shelves to the dolly frame, and to move said bin module from the dolly frame to the collection shelf when the dolly is positioned adjacent to the collection shelf and to uncouple the second coupler from the first coupler of said bin module; and (d) a first control unit configured to control operation of the first drive module and the first actuator, wherein the second coupler of the dolly comprises one or more arms movable by the first actuator to extend to and retract from said storage shelf when the dolly is positioned adjacent to the said storage shelf; and wherein the elevator includes an elevator frame, a second drive module configured to propel the elevator, the system for transporting inventory being characterised in that: the elevator comprises a second actuator configured to move a third coupler for holding a bin module both vertically and horizontally, and a second control unit that controls operation of the second drive module and the second actuator; wherein said third coupler is configured, as with the second coupler of the dolly, to couple to, and uncouple from, a corresponding coupler of one of the plurality of bin modules; and wherein said third coupler of the elevator is of the form of the second coupler of the dolly. the elevator comprises a second actuator configured to move a third coupler for holding a bin module both vertically and horizontally, and a second control unit that controls operation of the second drive module and the second actuator; wherein said third coupler is configured, as with the second coupler of the dolly, to couple to, and uncouple from, a corresponding coupler of one of the plurality of bin modules; and wherein said third coupler of the elevator is of the form of the second coupler of the dolly.