A modular shelving system has a first wall and a second wall. Extending between the first wall and the second wall is a plurality of rigid bridging members. Each of the walls has a base panel and a detachably connected ancillary panel. An upper profile of the base panel and a lower profile of the ancillary panel vertically interlock to form an interface. A plurality of apertures is formed along the interface when the panels are interlocked. A fastener, such as a screw, can be inserted through each of the plurality of apertures to detachably connect one of the walls to one of the plurality of bridging members. Additional walls and bridging members may be provided to form additional storage modules. Each wall may also be heightened by adding ancillary panels to form a highly accommodating expandable shelving system.