A transmission medium (plural transmission media) is a material substance (solid, liquid, gas, or plasma) that can propagate energy waves. For example, the transmission medium for sound received by the ears is usually air, but solids and liquids may also act as transmission media for sound.

The absence of a material medium in vacuum may also constitute a transmission medium for electromagnetic waves such as light and radio waves. While material substance is not required for electromagnetic waves to propagate, such waves are usually affected by the transmission media they pass through, for instance by absorption or by reflection or refraction at the interfaces between media.

The term transmission medium also refers to a technical device that employs the material substance to transmit or guide waves. Thus, an optical fiber or a copper cable is a transmission medium. Not only this but also is able to guide the transmission of networks.

A transmission medium can be classified as a:

Electromagnetic radiation can be transmitted through an optical media, such as optical fiber, or through twisted pair wires, coaxial cable, or dielectric-slab waveguides. It may also pass through any physical material that is transparent to the specific wavelength, such as water, air, glass, or concrete. Sound is, by definition, the vibration of matter, so it requires a physical medium for transmission, as does other kinds of mechanical waves and heat energy. Historically, science incorporated various aether theories to explain the transmission medium. However, it is now known that electromagnetic waves do not require a physical transmission medium, and so can travel through the "vacuum" of free space. Regions of the insulative vacuum can become conductive for electrical conduction through the presence of free electrons, holes, or ions.

Friedrich A. Kittler (June 12, 1943 – October 18, 2011) was a literary scholar and a media theorist. His works relate to media, technology, and the military.

Friedrich Adolf Kittler was born in 1943 in Rochlitz in Saxony. His family fled with him to West Germany in 1958, where from 1958 to 1963 he went to a natural sciences and modern languages Gymnasium in Lahr in the Black Forest, and thereafter, until 1972, he studied German studies, Romance philology and philosophy at the Albert Ludwigs University of Freiburg in Freiburg im Breisgau. During his studies, he was influenced by Jacques Lacan's and Michel Foucault's writings.

In 1976, Kittler received his doctorate in philosophy after a thesis on the poet Conrad Ferdinand Meyer. Between 1976 and 1986 he worked as academic assistant at the university's Deutsches Seminar. In 1984, he earned his Habilitation in the field of Modern German Literary History.

He had several stints as a Visiting Assistant Professor or Visiting Professor at universities in the United States, such as the University of California, Berkeley, the University of California, Santa Barbara and Stanford University.