Abstract: An article stacking apparatus, especially for stacking and forming packages of lumber, includes a plurality of elongate, parallel stacker arms for engaging and lifting courses of lumber onto a stack consisting of multiple courses to form a package. The stacker arms are oriented parallel to the direction of movement of lumber conveyed to the stacking apparatus, and transverse to the longitudinal axis of the lumber, and are spaced so that each piece of lumber spans at least two arms to be supported thereby. The stacker arms each have a rearward end carried by a drive chain disposed around a pair of spaced sprockets, and a forward end positioned to engage and lift a course of lumber as it is formed in the apparatus, for deposit of the course onto a stack.