  We study the universal properties of the phase diagram of QCD near the
critical point using the exact renormalization group. For two-flavour QCD and
zero quark masses we derive the universal equation of state in the vicinity of
the tricritical point. For non-zero quark masses we explain how the universal
equation of state of the Ising universality class can be used in order to
describe the physical behaviour near the line of critical points. The effective
exponents that parametrize the growth of physical quantities, such as the
correlation length, are given by combinations of the critical exponents of the
Ising class that depend on the path along which the critical point is
approached. In general the critical region, in which such quantities become
large, is smaller than naively expected.
