Abstract: A three-dimensional, curved building module comprises a saddle-shaped membrane having four connecting edges for joining with like building modules and four truncating edges. Connecting members are formed along the linear edge surfaces for joining the modules in edge-to-edge relation with one another. The building modules permit construction of complex, three dimensional forms which divide space into two distinct but intertwining volumes. The building modules may be used as a child's construction toy, playground structures, sculptures, architectural structures.