  This short theoretical review deals with some essential ingredients for the
understanding of the quantum Hall effect in graphene in comparison with the
effect in conventional two-dimensional electron systems with a parabolic band
dispersion. The main difference between the two systems stems from the
"ultra-relativistic" character of the low-energy carriers in graphene, which
are described in terms of a Dirac equation, as compared to the non-relativistic
Schr\"odinger equation used for electrons with a parabolic band dispersion. In
spite of this fundamental difference, the Hall resistance quantisation is
universal in the sense that it is given in terms of the universal constant
h/e^2 and an integer number, regardless of whether the charge carriers are
characterised by Galilean or Lorentz invariance, for non-relativistic or
relativistic carriers, respectively.
