  A general parametrization of the amplitudes for the rare two-body decays B ->
pi K is introduced, which makes maximal use of theoretical constraints arising
from flavour symmetries of the strong interactions and the structure of the
low-energy effective weak Hamiltonian. With the help of this parametrization, a
model-independent analysis of the branching ratios and direct CP asymmetries in
the various B -> pi K decay modes is performed, and the impact of hadronic
uncertainties on bounds on the weak phase gamma = arg(Vub*) is investigated.
