  In these lectures I explain how chiral symmetry of continuum QCD naturally
leads to a class of lattice regularisations known as twisted mass QCD (tmQCD).
As compared to standard Wilson quarks, its advantages are the absence of
unphysical zero modes, the possibility to circumvent lattice renormalisation
problems and automatic O(a) improvement. On the other hand, the physical parity
and flavour symmetries are explicitly broken. I discuss these aspects and then
turn to the theory in a finite space-time volume with Schroedinger functional
boundary conditions. Again, chiral transformations of the continuum theory may
be used as a guide to formulate an alternative lattice regularisation of the
Schr\"odinger functional, with interesting applications to renormalization
problems in QCD.
