Supermassive black holes are fundamental constituents of galaxies. Yet, many outstanding questions remain: how do supermassive black holes form? How do they initially grow? What is the fate of black hole binaries in different environments? In this talk, I will review the status of affairs behind this questions and I will highlighting some particular aspects, such as (i) the role of supermassive stars and quasi-stars in the direct collapse scenario, (ii) the state of the interstellar medium and the implications for mass transport in typical high-z galaxies as inferred from state of the art cosmological simulations, (iii) our attempts to improve accretion models for hydrodynamical large-scale simulations, and (iv) the evolution of massive black hole pairs in gas-rich and stellar-dominated environments.