Abstract: A toy building construction kit includes a plurality of floor defining elements, means for interconnecting the floor defining elements, a plurality of support pillar elements for interconnecting adjacent floors, and partition elements adapted to be received between the support pillar elements to define walls. A particularly rigid interconnection of the floor defining elements is achievd by using connecting elements and an arrangement of connecting lugs and recesses. The connecting lugs are T-shaped and fit tightly within corresponding recesses.