Observations of the cosmic microwave background (CMB) radiation have driven the current era of precision cosmology. Nevertheless, substantial information remains to be extracted from the primary CMB polarization anisotropies — including the signature of primordial gravitational waves — as well as the “secondary anisotropies” generated by effects between our vantage point and the surface of last scattering. The latter signals, including gravitational lensing and the thermal and kinematic Sunyaev-Zel’dovich (SZ) effects, also contain valuable astrophysical information about the distribution of baryons and dark matter at late times. I will present ongoing work to extract these signals in data from the Atacama Cosmology Telescope, as well as next-generation forecasts for the Simons Observatory (SO), which will begin observations in less than two years. Throughout, I will highlight novel foreground mitigation methods that I have developed, which are enabled by CMB observations at multiple frequencies. Applied to upcoming SO measurements of the SZ effects, CMB lensing, and primordial non-Gaussianity, these methods will yield transformative constraints on inflation, neutrino properties, and feedback mechanisms in galaxy formation and evolution. I will conclude with a look ahead to novel discovery space in measurements of the CMB energy spectrum.