A fulfillment system includes a storage structure arranged to house storage bins. The storage structure including first rails extending in a first direction and second rails extending in a second direction perpendicular that collectively forming a grid having a plurality of grid spaces. The system further includes a robot having a body including a plurality of sidewalls, a wheel assembly including a plurality of wheels arranged to move the body along the first rails and along the second rails, at least one bin holding device for holding order bins coupled to an interior surface of the body, a picking manipulator coupled to the body, and a first gripping tool coupled to the picking manipulator and moveable by the picking manipulator around an exterior of the body to pick inventory items from the storage bins.