  The development of improved algorithms for QCD on the lattice has enabled us
to do calculations at small quark masses and get control over the chiral
extrapolation. Also finer lattices have become possible, however, a severe
slowing down associated with the topology of the gauge fields has been
observed. This may prevent simulations of lattices fine enough for controlling
the continuum extrapolation. This conference contribution introduces the basic
concepts behind contemporary lattice algorithms, the current knowledge about
their slowing down towards the continuum and its consequences for future
lattice simulations.
