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Very Massive Stars (VMSs) with masses exceeding 100 solar masses are crucial for understanding chemical and energetic feedback in the Universe. These stars possess enormous luminosity-to-mass ratios and drive extremely strong stellar winds through radiation pressure on spectral transition lines. Despite their evolution and fate being largely dictated by wind mass loss, the mass-loss rates used in traditional stellar evolution models remain highly uncertain. This talk focuses on calculating hydrodynamically consistent non-LTE wind-atmosphere models of VMSs, testing our predictions against observations of known VMSs. I will present the first hydrodynamical atmosphere models for well-studied VMSs: R136a1, the most massive star known in the Local Universe, and R144, a double VMS spectroscopic binary system. Our models predict a steeper scaling of mass-loss rate with the luminosity-to-mass ratio compared to traditional prescriptions, indicating a sharp increase in mass loss toward the VMS end of the mass spectrum, with consequences for stellar evolution and the resulting black hole mass spectrum. VMS mass loss also impacts the metallicity threshold for the occurrence (or non-occurrence) of pair-instability supernovae, with implications for understanding the most massive stellar explosions in the early Universe.