We have investigated the insulator to metal transition in fluid deuterium using first principles simulations. Both density functional and quantum Monte Carlo calculations indicate that the electronic energy gap of the liquid vanishes at about ninefold compression and 3000 K. At these conditions the computed conductivity values are characteristic of a poor metal. These findings are consistent with those of recent shock wave experiments but the computed conductivity is larger than the measured value. From our ab initio results we conclude that the transition is driven by molecular dissociation rather than disorder and that both temperature and pressure play a key role in determining structural changes in the fluid. (C) 2004 American Institute of Physics.