The core of this article is a general theorem with a large number of specializations. Given a manifold N and a finite number of one-parameter groups of point transformations on N with generators Y, X (1) , · · · , X (d) , we obtain, via functional integration over spaces of pointed paths on N (paths with one fixed point), a one-parameter group of functional operators acting on tensor or spinor fields on N . The generator of this group is a quadratic form in the Lie derivatives L X (α) in the X (α) -direction plus a term linear in L Y .The basic functional integral is over L 2,1 paths x : T → N (continuous paths with square integrable first derivative). Although the integrator is invariant under time translation, the integral is powerful enough to be used for systems which are not time translation invariant. We give seven non trivial applications of the basic formula, and we compute its semiclassical expansion.The methods of proof are rigorous and combine Albeverio Høegh-Krohn oscillatory integrals with Elworthy's parametrization of paths in a curved space. Unlike other approaches we solve Schrödinger type equations directly,
Integrands and integrators.Splitting the quantity inside the integral sign into "integrator" and "integrand" belongs to the art of integration, but rules of thumb apply:-When the functional integral has its origin in physics try not to break up the action into, say, kinetic and potential contributions. On the other hand, do not hesitate to work with a potential which is a functional of a path rather than a function of its value (e.g. in equation (III.1), V is a functional of z, not a function of z(t)).-Look for a possible change of variable of integration; this may suggest a practical choice for the integrand.