Abstract: The Cosmic Microwave Background (CMB), the afterglow of Big Bang, gives us a snapshot of the early universe. Because temperature and polarization fluctuations record so much information about cosmological parameters, the CMB has become a cornerstone of modern cosmology. Curl-type (or "B-mode") polarization is particularly interesting because it probes gravity waves during inflation, and gives inflation's energy scale. However, polarized emission from the Milky Way is a serious contaminant. I will present a new model for the contamination, based on filamentary structure in the interstellar medium. Separately, we can also use the CMB as a backlight to learn about structure and astrophysical objects. For example, Sunyaev-Zeldovich scattering of CMB photons allow the detection of distant galaxy clusters, but dust emission complicates our interpretation. Gravitational lensing of the CMB by nearby structure is also a powerful tool to probe the expansion history of the universe and even measure the mass of the neutrino. I will discuss current and planned observations, including from the Advanced ACTpol project, Simons Observatory, and CMB-S4. We are exploring new ideas in data processing and analysis algorithms to better utilize the opportunities that the new, large datasets will present.
