A paramagnetic metal to nonmagnetic insulator transition at T-MIT = 210 K is reported for the beta-pyrochlore oxide CsW2O6, accompanied by a first order structural transition that creates < 110 > oriented chains in the pyrochlore lattice. Comparison of CsW2O6, which has 1 electron per 2 W sites, to the fully d(0) analog CsTaWO6 shows that the transitions are electronically driven. Corefinement of high resolution synchrotron x-ray and neutron diffraction data shows that the structural distortion that creates the W chains cannot be attributed to simple charge or orbital ordering. Density functional theory calculations suggest that the phase transition is driven by a sharply peaked electronic density of states near the Fermi energy in the cubic beta-pyrochlore phase. A further electronic instability is required to create the insulating ground state. DOI: 10.1103/PhysRevLett.110.166402