Abstract This manuscript develops a systematic higher-order functional analysis. The central idea is that nonlinear functionals are not merely evaluated or linearized, but organized into higher-order functional spaces whose coordinates are intrinsic invariant packages: critical sets, Hessian spectra, variational profiles, symmetry quotients, moduli data, stochastic laws, and reconstruction maps. A first-order nonlinear functional space is replaced by a second-order quotient space of invariant fibers; iterating this construction produces a tower of higher-order functional spaces whose infinite-order limit carries a complete geometric, spectral, and operator-algebraic structure. The theory is applied to deterministic and stochastic nonlinear variational PDE. For every admitted variational PDE, the nonlinear solution is exactly reconstructed from an infinite-order coordinate solution by the master formula u=P∞(Φ∞),u=P∞(Φ∞), where Φ∞Φ∞ solves a closed linear coordinate equation and P∞P∞ reconstructs the original state. Existence, stability, and regularity are encoded in a single ESR ledger: incidence gives existence, retained spectral sign gives stability, and tower-level control gives regularity. The same framework extends to random functionals and stochastic PDE through measurable invariant packages and direct-integral spectra. Classical stability problems—from nonlinear Schrödinger equations to Kerr black holes—are recovered as second-order spectral computations. Under quantitative tower and spectral-tail estimates, the projected computation is polynomial in the requested tolerance and improves monotonically with retained order. The result is a unified language in which nonlinear functionals, deterministic variational PDE, stochastic variational PDE, stability spectra, regularity thresholds, analytic reconstruction, and polynomial projected computation are components of one higher-order functional architecture. Keywords Higher-Order Functional Analysis; Nonlinear Functional Spaces; Invariant Packages; Fiber Quotients; Variational PDE; Spectral Rigidity; Stochastic PDE; Infinite-Order Linearization; Exact Reconstruction; ESR Ledger; Projection Computation; Topological Coordinates; Geometric Linearization