I will describe how I use mm-wavelength instruments (both spectrometers and photometers) to explore our universe across cosmic time. I will discuss instruments such as SPT-pol, CMB-S4, TIME, and future even more powerful mm-wavelength spectrometers that will allow us to probe the universe, from the first fractions of a second after the big bang to the present day.  These new instruments and the detector technologies being developed in the field can be used to study 1) inflation and neutrinos via the CMB; 2) the epoch of reionization; and 3) galaxies at the peak of star formation.