The goal of this IHES school is to prepare students to make contributions to the study of cosmological correlations, both in the early and late universe. Theoretical cosmology as a discipline is increasingly crossing traditional subfield boundaries within high-energy physics. As a result, the full spectrum of topics and expertise students require cannot be simply contained in a single course. This school aims to fill this gap by providing a holistic viewpoint on the diverse set of topics that students need to know, with an eye towards their applications in cosmology. There has been a remarkable amount of progress in the study of cosmological quantum field theory in the last few years, and a dedicated school focused on the diverse set of skills needed to contribute is much needed. The school will have a set of courses given by world leaders in the subject, with the first week focused on EFT and bootstrap methods to compute cosmological correlators, and the second week devoted to more advanced topics and connections at the interface of particle theory and cosmology.