  We present a new approach to path integral Monte Carlo (PIMC) simulations
based on the worm algorithm, originally developed for lattice models and
extended here to continuous-space many-body systems. The scheme allows for
efficient computation of thermodynamic properties, including winding numbers
and off-diagonal correlations, for systems of much greater size than that
accessible to conventional PIMC. As an illustrative application of the method,
we simulate the superfluid transition of Helium-four in two dimensions.
