Using recent advances in the nonparametric estimation of continuous-time processes under mild statistical assumptions as well as recent developments on nonparametric volatility estimation by virtue of market microstructure noise-contaminated high-frequency asset price data, we provide (i ) a theory of spot variance estimation and (ii ) functional methods for stochastic volatility modelling. Our methods allow for the joint evaluation of return and volatility dynamics with nonlinear drift and di¤usion functions, nonlinear leverage e¤ects, jumps in returns and volatility with possibly state-dependent jump intensities, as well as nonlinear riskreturn trade-o¤s. Our identi…cation approach and asymptotic results apply under weak recurrence assumptions and, hence, accommodate the persistence properties of variance in …nite samples. Functional estimation of a generalized (i.e., nonlinear) version of the square-root stochastic variance model with jumps in both volatility and returns for the S&P500 index suggests the need for richer variance dynamics than in existing work. We …nd a linear speci…cation for the variance's di¤usive variance to be misspeci…ed (and inferior to a more ‡exible CEV speci…cation) even when allowing for jumps in the variance dynamics.