  We present a microscopic study of the quantum fluctuations of the
superconducting order parameter in thin homogeneous superconducting wires at
all temperatures below $T_C$. The rate of quantum phase slip processes
determines the resistance $R(T)$ of the wire, which is observable in very thin
wires, even at low temperature. Furthermore, we predict a new low temperature
metallic phase below a critical wire-thickness in the 10nm range, in which
quantum phase slips proliferate.
