We are witnessing an exciting revolution in our understanding of the first billion years of cosmic history. The launch of the JWST has enabled the discovery of galaxies in the first few hundred million years, and their detailed characterization in terms of chemical enrichment, stellar populations, nuclear black hole properties, morphologies, and environment is ongoing. In addition to these stunning discoveries, there have also been recent probes of the dust content of galaxies in the first billion years with ALMA, and robust theoretical predictions are also essential for interpreting future observations with ELTs and “deep-wide field” observations with the Nancy Grace Roman telescope. At the same time, GAIA and SDSS-V are probing the chemical abundances of individual stars in our own Galaxy and in nearby galaxies, which provide complementary “fossil evidence” on the properties of the first stars and how early galaxies were enriched with the heavy elements that eventually made life on Earth possible. This wealth of data has the potential to paint a picture of unprecedented clarity and detail of the first billion years of cosmic evolution — provided we have robust and detailed theoretical models with which to interpret and stitch them together. The goal of this program is to provide a unique forum for theorists and observers specializing in different subfields to interact intensively with each other developing links between several synergistic areas, including star formation, stellar evolution, chemistry, radiation, gas physics, and cosmology.