This first volume is concerned with the analytic derivation of explicit
formulas for the leading-order Taylor approximations of (local)
stochastic invariant manifolds associated with a broad class of
nonlinear stochastic partial differential equations. These
approximations take the form of Lyapunov-Perron integrals, which are
further characterized in Volume II as pullback limits associated with
some partially coupled backward-forward systems. This pullback
characterization provides a useful interpretation of the corresponding
approximating manifolds and leads to a simple framework that unifies
some other approximation approaches in the literature. A self-contained
survey is also included on the existence and attraction of one-parameter
families of stochastic invariant manifolds, from the point of view of
the theory of random dynamical systems.