Hydrogen reaches the mimimum electrical conductivity of a metal at 140 GPa (1.4 Mbar), 0.6 g cm(-3) (ninefold compression of initial liquid-H(2) density) and 3000 K in the fluid phase. The quest for metallic hydrogen over the past 100 years is reviewed briefly. Possible scientific and technological uses of metastable solid metallic hydrogen (MSMH) are speculated upon in the unlikely event that the metallic fluid can be quenched to MSMH at ambient pressure and temperature: a quantum, mostly diatomic, metallic solid with novel physical properties, including room-temperature superconductivity; a very light-weight structural material; a fuel, propellant, or explosive, depending on the rate of release of stored energy; a dense fuel for higher energy yields in inertial confinement fusion; and an aid in the synthesis of novel hard materials. Some of the formidable difficulties to synthesize MSMH are discussed.