A knock-down shelving unit is composed of four identical short panels, each having a slot extending perpendicularly from the middle of one edge to an inner end half way across the panel, and at least four longer panels, each having three similar slots. The parts of the panels extending from the inner ends of the slots to the opposite edges serve as connecting elements. The panels are interlocked by engaging the slots and connecting elements to form a lattice. In the lattice, where an end of a panel meets the end of another panel, a tongue formed on the end of each panel fits a recess formed in the end of the other panel. In an eight panel shelving unit, only two kinds of panels are required. In a shelving unit composed of ten or more panels, only three kinds of panels are required.