Otto Lehmann (13 January 1855 in Konstanz, Germany – 17 June 1922 in Karlsruhe) was a German physicist and "father" of liquid crystal.

Otto was the son of Franz Xavier Lehmann, a mathematics teacher in the Baden-Wurtemberg school system, with a strong interest in microscopes.

Between 1872 and 1877, Lehmann studied natural sciences at the University of Strassburg and obtained the Ph.D. under crystallographer Paul Groth.

Otto used polarizers in a microscope so that he might watch for birefringence appearing in the process of crystallization.

As Dunmur and Sluckin(2011) say The article "On Flowing Crystals" that Lehmann wrote for Zeitschrift für Physikalische Chemie addresses directly the question of phase of matter involved, and leaves in its wake the science of liquid crystals.