Abstract: The existence of luminous quasars hosting billion-solar-mass supermassive black holes (SMBHs) at z>7, when the Universe was less than 800 million years old, challenges our understanding of SMBH formation. Recent JWST discoveries of abundant broad-line AGNs further complicate the situation. In the context of hierarchical structure formation, various cosmological simulations suggest that massive SMBHs in the early Universe can form from large seeds. These models generally predict that the earliest SMBHs are hosted by massive galaxies and reside in the most biased dark matter halos, situated in overdense regions. However, rigorously testing these theories remains difficult. In this talk, I will present the major efforts I have been leading with new JWST observations, aiming to test these theories in detail by resolving the long-standing questions of whether these SMBHs reside in massive galaxies and whether they are hosted by biased dark matter halos. Furthermore, I will highlight how we are entering an exciting new era in understanding the formation of early SMBHs and galaxies within a cosmological context.