Computational studies of dialkyne and polyalkyne structures, stabilities, and reactivities are described.  Density functional theory and CASSCF calculations have been applied to 1) the structures and strain energies of Diederich's expanded polyhedranes, containing diyne units between each vertex, 2) stabilities of conjugated diynes and evidence for conjugative stabilization, and 3) reactivities in dimerization and polymerization reactions of diynes and polyynes.