Abstract: A modular system for forming without tools a variety of 3-dimensional structures comprises panels (10), and connectors (13, 14), and locking bridging members (30) for assembling the panels (10) together in a desired configuration. The panels can be disconnected so that the erected structure can be disassembled with ease for future reuse. The system can be used to erect children's playhouses made of polymer materials, as well as in a large variety of other applications to create 3-dimensional objects requiring rapid positive construction without tools.