The quasi-static elasticity (Gibbs' elasticity) of sea surface films collected in North American coastal waters has been examined using a large number of surface pressure-area isotherms. The films examined show considerable variability in elastic properties. Differences among films appear to be the result of chemical variability due to differences in source; they are also affected by dynamic physical processes (e.g., film compression). Elasticities of adsorbed films from subsurface and microlayer water are observed to exhibit a bimodal distribution at 0.5 mN m-1 reference spreading pressure; films from organized banded slicks are shown to have generally higher elastic moduli. Mechanisms of surface selectivity and competitive adsorption are suggested to explain this effect; results of film aging and work hardening studies are presented in support. Significant hysteresis effects are observed for cyclical compression and dilation of the films suggesting the prevalence of relaxation processes that lead to compositional changes and higher elastic moduli. Field measurements of capillary and ripple spectra are presented to infer information on wave damping and dynamic viscoelasticity. Results obtained in regions where surface convergence is absent imply damping enhancement over a broad frequency range consistent with theory for films of low elastic moduli. Films found in surface convergence zones, the result of surface upwelling, exhibit damping enhancements consistent with higher elastic moduli. Damping maxima are observed in multiple frequency bands; this banding is not readily explained with current theories. Results similar to these have been observed in laboratory studies with other chemical systems. In both the laboratory and field experiments, the tendency of the films to group into a few subsets with similar surface characteristics implies that natural films might be modeled by a small number of representative end members. This would facilitate remote sensing applications by providing a basis for determining the effects of films on surface waves under various conditions (e.g., diurnal variation, history of variability of wind stress). ¿ American Geophysical Union 1993