We present our recent progress pertaining to the synthesis and analysis of bianisotropic linear and nonlinear metasurfaces. These developments are based on the generalized sheet transition conditions (GSTCs), which provide a very complete and general method for modeling metasurfaces. Specifically, we present our most recent research, which includes the control of radiation pressure at both the micro- and macroscopic scales, the analysis of second-harmonic scattering from nonlinear metasurfaces, and the surface-wave dispersion retrieval method for bianisotropic metasurfaces in symmetric and asymmetric environments.