The interstellar medium of high-redshift galaxies

State-of-the-art facilities such as ALMA and JWST in recent years have revolutionized our understanding of the interstellar medium (ISM) of both star-forming and quiescent galaxies at high redshift. It is now feasible to investigate the physical conditions, the morphology, and the kinematics of the ISM from cosmic noon to cosmic dawn in a spatially-resolved fashion down to a comparable level of details to that reached in the local Universe. It also became possible to detect and study the ISM properties of quiescent galaxies at cosmic noon, shedding light on the reasons why they stop forming stars. I will discuss recent results on these topics, with an observational perspective, focusing on open questions, on the findings enabled by ALMA in synergy with the other observatories, and on the still debated challenges.