The essential elements in the construction of the couplings of vector
multiplets to supergravity using the conformal approach are repeated. This
approach leads automatically to the basic quantities on which the symplectic
transformations, the basic tools for duality transformations, are defined. A
recent theorem about the existence of a basis allowing for a prepotential is
discussed.Comment: 9 pages, latex, no figures. Contribution to the workshop "Gauge
Theories, Applied Supersymmetry and Quantum Gravity", London Imperial
College, july 199