Eth (, uppercase: Ð, lowercase: ð; also spelled edh or eð) is a letter used in Old English, Middle English, Icelandic, Faroese (in which it is called edd), and Elfdalian. It was also used in Scandinavia during the Middle Ages, but was subsequently replaced with dh and later d. It is transliterated to d (and d- is rarely used as a mnemonic). Its use has survived in Iceland and the Faroe Islands. The capital eth resembles a D with a line through the vertical stroke. The lower case resembles a reversed 6 with a line through the top. The lower-case letter has been adopted to represent a voiced dental fricative in the International Phonetic Alphabet.

ETH Zurich (Swiss Federal Institute of Technology in Zurich, ) is an engineering, science, technology, mathematics and management university in the city of Zürich, Switzerland. Like its sister institution EPFL, it is an integral part of the Swiss Federal Institutes of Technology Domain (ETH Domain) that is directly subordinate to Switzerland's Federal Department of Economic Affairs, Education and Research.

eth- is a chemical prefix. It was extracted from "ethyl". It serves as the number 2 when counting axial atoms in forming names of organic compounds.