Abstract: A reusable tool for the installing of horizontal overlapping siding boards on a building framework. The disclosed tool comprises an elongated base member including a first end portion defining means for releasably engaging the upper edge of a siding board such that the base member depends from such upper edge and lies proximate to the exposed outer face of the board. The second end portion of the base member defines the lower extremity of the tool and pivotally receives an elongated arm means which is movable between multiple positions relative to the base member. In one such position, the arm is substantially parallel to the base member and in such position defines with the base a channel within which the bottom edge of a siding board is received and held relative to the subjacent board to which the siding tool is engaged.