An apparatus for installing siding on a wall by a single person is disclosed. The apparatus includes a siding hook and a gauge for positioning a length of siding at a predetermined degree of overlap over an installed length of siding. The gauge comprises an elongate slide bar and a stop block slidably mounted on the slide bar. The stop block is clamped to the slide bar by screws which thread into holes formed in the stop block. The heads of the screws are entrapped within the stepped slot of the slide bar. Both the slide bar and the stop block have flat surfaces devoid of projections which could mar siding, and rounded or beveled edges and corners. The siding hook is S-shaped, formed from thin sheet metal or plastic, and configured to overhang the installed siding while supporting a length of siding being installed over installed siding.