  Lattice QCD was invented thirty years ago but only in the last few years has
it finally fulfilled its promise as a precision tool for calculations in hadron
physics. This review will cover the fundamentals of discretising QCD onto a
space-time lattice and how to reduce the errors associated with the
discretisation. This 'improvement' is the key that has made the enormous
computational task of a lattice QCD calculation tractable and enabled us to
reach the recent milestone of precision calculations of simple 'gold-plated'
hadron masses. Accurate decay matrix elements, such as those for leptonic and
semileptonic decays of heavy mesons needed by the B factory experimental
programme, are now within sight. I will describe what goes into such
calculations and what the future prospects and limitations are.
