One of the legacy results of the Hubble Space Telescope is the discovery that supermassive black holes inhabit the centers of all massive galaxies, and these black holes appear to have a symbiotic relationship with their host galaxies. One of the keys to understanding this relationship involves constraining the masses of the black holes. However, black hole mass measurements are difficult to achieve because they require direct observations of the invisible black hole's gravitational influence on luminous tracers (stars or gas). A few different techniques have been developed over the last 25 years to meet this goal. One technique, known as reverberation mapping, is exclusively applicable to active black holes but may be used for even the most distant quasars in our universe, providing a way to study black holes across history. However, the most widely used technique in the local universe requires exquisite spatial resolution and is based on observations of the bulk motions of stars deep in the nucleus of a (usually inactive) galaxy. I will introduce these techniques and describe our ongoing program to identify a small sample of galaxies where multiple black hole mass techniques can be applied to each galaxy. This effort includes our recently-approved JWST ERS program, as well as programs carried out on multiple moderate- and large-aperture ground-based telescopes. The results of this work will allow us to directly test these independent mass measurement techniques against each other, investigating whether the masses of all black holes, both near and far, are on the same scale and thus having implications for our understanding of the evolution of galaxies across the ~13 billion year history of the universe.