A shelf divider is designed for use on a shelf having rows of apertures extending along the front and back of the shelf. The divider is made of plastic sheet with a vertical divider panel and a horizontal attachment panel. A tongue at the front end of the attachment panel is inserted in a selected aperture at the front of the shelf. A perforation in the attachment panel aligned with the tongue is positioned to overlie a corresponding aperture at the back of the shelf. To releasably attach the divider to the shelf, a push-in plastic pin is inserted in the perforation and corresponding aperture. The divider is formed with tongues and perforations at both ends to make it reversible.