Heinrich Geissler (May 26, 1814 - January 24, 1879) was a German physicist.

Educated by his father as a glassblower and gifted for the design and engineering, Geissler is most remembered for the invention of sealed glass tubes (called Geissler tubes) from which he demonstrated with Julius Plucker emission of a bluish glow by exciting the gas with an induction coil. It was not uncommon for these tubes to display elaborate and artistic shapes, adding much to the optical effect. The device can be regarded as an ancestor of the fluorescent lamp. It was improved by Sir William Crookes and is thus commonly called a Crookes tube.