A modular storage system capable of mounting storage fixtures such as shelves, drawers, rods, desks, hampers, trash cans and the like in various configurations without the use of tools and fastener hardware. The system includes vertical side panels capable of being mounted to a horizontal support rail, which is attached to a wall, in various configurations allowing the system to be mounted and rearranged against the wall without the use of tools and hardware. The vertical side panels include a plurality of support cleats that mate with the storage fixtures and provide for self-locking of the storage fixtures in the system so that they can be mounted and rearranged without the use of tools and hardware.