Abstract: In a modular-design toy system for preparing buildings, vehicle and landscape structures etc., comprising building elements of plastic material, which are releasably attachable to each other by snap-fastener connecting elements, provision is made, with a view to obtaining a true-to-nature appearance at a reasonable cost and durable and constant snap-fastening properties, for connecting elements having first snap-in elements on one side for the easily releasable attachment to corresponding first locking recesses on the building elements and having second snap-in devices on the other side for the hard-to-release attachment to corresponding second locking recesses of the building elements.