In this dissertation, we aim to understand the mechanical properties of thin films and classes of wrinkle patterns of polymer films using capillary wrinkling. We discuss four independent research subjects. In the first project, we measure the thickness (t) dependence of Young’s modulus (E) of polymer thin films. Thin films were measured from bulk thicknesses down to thickness less than the radius of gyration (6 nm). E does not show any systematic change with t, although an increase in modulus was found for the thinnest poly(styrene) (PS) film. The second topic is stretching (Y) and bending (B) moduli of PS/poly(methyl methacrylate) (PMMA) and PS/gold (Au) bilayer films inferred from wrinkle patterns. The Y, B, and wrinkle patterns for PS/PMMA and PMMA/PS bilayers were not affected by the difference in surface energies nor the ratio of the thicknesses. However, the normalized length of wrinkles (L/a) from PS/Au and Au/PS showed no significant variation against Y while Au/PS increased in the number of wrinkles when B ≤ ~ 10-12 N·m. We also investigated the concentration and thickness dependence of the composite modulus (Ec) of PS-gold nanoparticles (GNPs) nanocomposites. Different wt% of 124 kg/mol Mw PS capped 12 nm diameter GNPs were mixed with a 97 kg/mol Mw PS matrix (30 nm ≤ tPS-GNPs ≤ 148 nm). An increase in the L/a value was found for tPS-GNPs ~ 148 nm with 13 wt% loading. The normalized number of wrinkles (N/a0.5) in a 30 nm thick film with 5 wt% GNPs loading was found to increase by 2.7 times over that of PS homopolymer, but showed a decrease when the GNPs loadings were increased. As tPS-GNPs ≥ 102 nm, N/a0.5 became ~ (Et3)-1/4, similar to PS homopolymer. Furthermore, Ec was observed to be double that of PS homopolymer when tPS-GNPs ≥102 nm with 13 wt% GNPs loading. Finally, we observed classes of wrinkle patterns from different PS film thicknesses: Single mode in regime (i) t ≥ 600 nm, period-doubling in regime (ii) 50 nm ≤ t ≤ 600 nm, and Double mode in regime (iii) t ≤ ~ 50 nm.