  This is a solicited whitepaper for the Snowmass 2021 community planning
exercise. The paper focuses on measurements and science with the Cosmic
Microwave Background (CMB). The CMB is foundational to our understanding of
modern physics and continues to be a powerful tool driving our understanding of
cosmology and particle physics. In this paper, we outline the broad and unique
impact of CMB science for the High Energy Cosmic Frontier in the upcoming
decade. We also describe the progression of ground-based CMB experiments, which
shows that the community is prepared to develop the key capabilities and
facilities needed to achieve these transformative CMB measurements.
