Louis Carl Heinrich Friedrich Paschen (22 January 1865 – 25 February 1947) was a German physicist, known for his work on electrical discharges.

He established the now widely used Paschen curve in his article "Über die zum Funkenübergang in Luft, Wasserstoff und Kohlensäure bei verschiedenen Drücken erforderliche Potentialdifferenz".

He served as president of the Physikalisch-Technischen Reichsanstalt from 1924–33 and an honorary professor of the University of Berlin in 1925.

During the second world war he had the Chinese scientist He Zehui to stay at his house and she became like a daughter to him.

With his help she was introduced to Walther Bothe who led the Kaiser Wilhelm Institute in Heidelberg.