The local correlation between black hole mass and galaxy mass indicate that black hole accretion and galaxy formation have been tightly connected during the cosmic times, and that nuclear activity and star formation have affected each other. Various theoretical models have been proposed to explain the local black hole-galaxy relation, invoking various physical processes and scenarios. I will discuss the observational evidences for the galaxy-black hole coevolution at high redshift and how these evidences compare with the predictions of theoretical models (e.g. star formation in AGN hosts, feedback effects, metal enrichment, evolution of the BH-galaxy relation). I will show that some of the models predictions are confirmed by observations of high-z AGNs... however observations have also opened some important issues that are difficult to explain within any of the theoretical scenarios currently proposed.