William Weber Coblentz (1873 – September 15 1962) was an American physicist. He worked at the National Bureau of Standards from 1905 until 1945.

He was the first to verify Planck's Law. He also conducted astronomical research, measuring the temperature of planets and the radiation of stars. He is therefore regarded as the founder of astronomical infrared spectroscopy.

Together with Carl Lampland he measured large differences between the day and night temperatures on Mars.

A crater on Mars was named in his honor.