How stars and galaxies form and evolve is one of the fundamental questions in the field of astrophysics. Star formation in the early Universe occurred at a higher rate than the present day and often in extremely dusty environments. The brightest galaxies are known as ultraluminous galaxies and are the product of galaxy mergers. These galaxies are hidden to optical telescopes and require observations in the infrared/sub-millimeter range.  ZEUS-2 is the second generation Redshift (Z) and Early Universe Spectrometer (P.I. Gordon Stacey, Cornell University).  It is designed to study star formation in galaxies from their birth in the early Universe around 12-billion years ago, through to the present day. In the “local” universe (z < 0.1) ZEUS-2 targets the warm molecular gas cooling lines of ¹²CO(J=8-7, 7-6, and 6-5), and ¹³CO(6-5) and the neutral atomic carbon lines  [CI] 370 micron and 610 micron. In the early universe (z>1) the telluric windows correspond to the redshifted fine structure lines of [CII] 158 micron, [OIII] 88 micron, [OI] 63 micron, and [NII] 122 micron and 205 micron. I will demonstrate how far-infrared and submillimetre observations can be used to investigate the physical properties of the interstellar medium in a sample of galaxies. In the process I will highlight some of the results from the ZEUS-2 consortium.