Abstract: Octahedral structures using compression and tension members are joined along a common edge to form adjacent tetrahedrals, to produce a rigid or flexible "octet" structural system. Pairs of tension members interconnecting corners of the octahedra may be lengthened and shortened to provide controlled hinging of the adjacent octahedra about the common edge. The octahedra may be collapsed into a linear bundle of struts and tension members or cables by lengthening the tension cables and pivoting the struts into alignment at their junction. Octahedral/tetrahedral structures may extend for many modules in three directions to form an extended structure, with openings provided where desired by omtting one or more octahedra.