Abstract: An instantaneous, snap-open, four-sided carton adapted to be stacked flat and snapped open. The carton is formed from a blank of cardboard and scored to define a plurality of parallel panels forming the vertical or longitudinal sides of the carton. There are two oppositely arranged flaps which form the bottom of the carton when it is open. These bottom flaps are diagonally scored to form fold lines or troughs and one of the flaps is diagonally longer than the other. When the carton is folded flat, the respective scored flaps are folded along the scored lines so that the parts of the respective flaps at opposite sides of the score lines are folded together or onto themselves. As the opposite free corners of the flattened carton are pressed toward each other, the scored flaps open up, first forming V-shaped troughs. The trough of the shorter flap enters the trough of the longer trough and is guided inwardly by the longer trough until the carton is fully open.