Polarization links atomic scale charge rearrangements to the emergent behavior of quantum materials underlying their dielectric, optical, piezoelectric, and ferroelectric properties. In this talk, I will discuss how first principles calculations can be used to understand and predict polarization, from the modern theory of polarization to its practical implementation within density functional theory and finite-field methods. I will present recent work from our group on polarization at surfaces, interfaces, defects, and other low-symmetry environments, with examples from oxide dielectrics and ferroelectrics relevant to quantum technologies. These case studies illustrate how first principles calculations connect atomic-scale structure and electronic properties to experimentally measurable behavior. I will conclude by discussing recent efforts to improve the reliability of computational predictions through uncertainty quantification and by considering how data-driven methods can help identify new materials with tunable polarization response.