A symplectic covariant formulation of special Kahler geometry in superconformal calculus

We present a formulation of the coupling of vector multiplets to N = 2 supe rgravity which is symplectic covariant (and thus is not based on a prepoten tial) and uses superconformal tensor calculus. We do not start from an acti on, but from the combination of the generalized Bianchi identities of the v ector multiplets in superspace, a symplectic definition of special Kahler g eometry, and the supersymmetric partners of the corresponding constraints. These involve the breaking to super-Poincare symmetry, and lend to on-shell vector multiplets. This symplectic approach gives the framework to formulate vector multiplet couplings using a weaker defining constraint for special Kahler geometry, w hich is an extension of older definitions of special Kahler manifolds for s ome cases with only one vector multiplet.