  I review the theoretical foundations, properties as well as the simulation
results obtained so far of a variant of the Wilson lattice QCD formulation:
Wilson twisted mass lattice QCD. Emphasis is put on the discretization errors
and on the effects of these discretization errors on the phase structure for
Wilson-like fermions in the chiral limit. The possibility to use in lattice
simulations different lattice actions for sea and valence quarks to ease the
renormalization patterns of phenomenologically relevant local operators, is
also discussed.
