A shelving system includes a frame with vertical frame members and cross braces, a shelf with three-sided perimeter groove and under-shelf groove, a wire perimeter shelf support engaging the perimeter groove and vertical frame members, and a wire under-shelf support constructed to engage the under-shelf groove and the vertical legs in a stable arrangement. The assembled shelving system does not require tools or separate fasteners for assembly, and assembly is quick, easy and intuitive, yet allows for flexibility, customization, and adaptation for different uses and desired aesthetics. A variety of very different shelving systems can be constructed by purchasing different frames, shelves, and accessories. The system can be leaned against a wall at an angle, or fastened vertically against a wall. Shelves are angularly adjustable, height adjustable, and replaceable. A pair of systems angled against each other form a free standing arrangement, and can support a header panel therebetween.