We study the physical and chemical conditions of the interstellar medium (gas and dust) and how they regulate star formation across galaxies over cosmic time. How galaxies form stars and get enriched with heavy elements as the building blocks of planetary systems and eventually life are central questions. An integral part of our work is to understand how spectral line and continuum emission from atoms, molecules and dust grains can be used to address such questions. We use observations from mostly radio astronomical facilities as well as modeling approaches to achieve these goals.