A stacking device for flat objects standing upright stacks the objects to form a stack which increases in a stacking direction. The stacking device includes at least one stacking point at which the objects are respectively added to the stack. The stacking device also includes at least one stack holder drive with which at least one stack holder receiving the stack can be moved in the stacking direction relative to the stacking point. A stack holder for a stack of flat objects standing upright and a sorting system for sorting flat objects including a plurality of stacking devices, are also provided.

According to a method for forming packs of flat bags, a continuous line of bags moving in an oriented direction of advance is received. The bags are moved onto a receiving table on which the bags are stacked while being stopped from moving in the oriented direction of advance by an abutment. The continuous line of bags is converted into a line of overlapped bags before stacking the latter, and the bags are separated on the receiving table by separating means comprising a separating device. During this operation, a separating device is inserted by a movement in the separating direction perpendicular to the plane of the bags between a preceding bag and a following bag in the overlapped line in such a way that, when the following bag stops against the abutment, it is supported at least partially by the separating means.