Abstract: The James Webb Space Telescope (JWST) has rapidly transformed our view of galaxy and black hole formation within the first billion years of cosmic history, revealing a population of surprisingly luminous, chemically evolved galaxies and abundant accreting black holes at very early times. These discoveries challenge long-standing theoretical expectations and call for a reassessment of how structure assembled in the young universe.

In this colloquium, we present a joint observational and theoretical perspective on the emerging picture of high-redshift (z ≳ 6–10) galaxies and AGN in the JWST era. We will first highlight recent observational results from JWST, including constraints on galaxy growth and the nature of early black hole activity. We will then discuss how these findings are being interpreted within theoretical models of galaxy formation and reionization, and what tensions, and opportunities, they reveal.

By combining these complementary approaches, we aim to outline a coherent framework for understanding the first billion years, and to identify key questions and observational tests that will define the next phase of JWST-driven exploration of the early universe.