  We describe a global approach to the study of duality transformations between
antisymmetric fields with transitions and argue that the natural geometrical
setting for the approach is that of gerbes, these objects are mathematical
constructions generalizing U(1) bundles and are similarly classified by
quantized charges. We address the duality maps in terms of the potentials
rather than on their field strengths and show the quantum equivalence between
dual theories which in turn allows a rigorous proof of a generalized Dirac
quantization condition on the couplings. Our approach needs the introduction of
an auxiliary form satisfying a global constraint which in the case of 1-form
potentials coincides with the quantization of the magnetic flux. We apply our
global approach to refine the proof of the duality equivalence between d=11
supermembrane and d=10 IIA Dirichlet supermembrane.
