  This is an expanded version of lecture notes, delivered at the XCIII Les
Houches Summer School (August 2009). Our aim is to present three very specific
topics: (i) The consequences of the loss of chiral symmetry in the Wilson
lattice regularization of the fermionic action and its recovery in the
continuum limit. The treatment of these arguments involves lattice Ward
identities. (ii) The definition and properties of mass independent
renormalization schemes, which are suitable for a non-perturbative computation
of various operator renormalization constants. (iii) The modification of the
Wilson fermion action, by the introduction of a chirally twisted mass term
(known as twisted mass QCD - tmQCD), which results to improved
(re)normalization and scaling properties for physical quantities of interest.
