Traditional English renderings of Greek names originated from Roman systems established in antiquity. The Roman alphabet itself was a form of the Cumaean alphabet derived from the Euboean script that valued Χ as /ks/ and Η as /h/ and used variant forms of Λ and Σ that became L and S. When this script was used to write the classical Greek alphabet, ⟨κ⟩ was replaced with ⟨c⟩, ⟨αι⟩ and ⟨οι⟩ became ⟨æ⟩ and ⟨œ⟩, and ⟨ει⟩ and ⟨ου⟩ were simplified to ⟨i⟩ (more rarely—corresponding to an earlier pronunciation—⟨e⟩) and ⟨u⟩. Aspirated consonant like ⟨θ⟩, ⟨φ⟩, initial-⟨ρ⟩, and ⟨χ⟩ simply wrote out the sound: ⟨th⟩, ⟨ph⟩, ⟨rh⟩, and ⟨ch⟩. Because English orthography has changed so much from the original Greek, modern scholarly transliteration now usually renders ⟨κ⟩ as ⟨k⟩ and the diphthongs ⟨αι, οι, ει, ου⟩ as ⟨ai, oi, ei, ou⟩. Modern scholars also increasingly render ⟨χ⟩ as ⟨kh⟩.
The sounds of Modern Greek have diverged from both those of Ancient Greek and their descendant letters in English and other languages. This led to a variety of romanizations for names and placenames in the 19th and 20th century. The Hellenic Organization for Standardization (ELOT) issued its system in cooperation with the International Organization for Standardization (ISO) in 1983. This system was adopted (with minor modifications) by the United Nations' Fifth Conference on the Standardization of Geographical Names at Montreal in 1987, by the United Kingdom's Permanent Committee on Geographical Names for British Official Use (PCGN) and by the United States' Board on Geographic Names (BGN) in 1996, and by the ISO itself in 1997. Romanization of names for official purposes (as with passports and identity cards) were required to use the ELOT system within Greece until 2011, when a legal decision permitted Greeks to use irregular forms (such as "Demetrios" for Δημήτριος) provided that official identification and documents also list the standard forms (as, for example, "Demetrios OR Dimitrios"). Other romanization systems still encountered are the BGN/PCGN's earlier 1962 system and the system employed by the American Library Association and the United States' Library of Congress.
"Greeklish" has also spread within Greece itself, owing to the rapid spread of digital telephony from cultures using the Latin alphabet. Since Greek typefaces and fonts are not always supported or robust, Greek email and chatting has adopted a variety of formats for rendering Greek and Greek shorthand using Latin letters. Examples include "8elo" and "thelw" for θέλω, "3ava" for ξανά, and "yuxi" for ψυχή.
The following tables list several romanization schemes from the Greek alphabet to modern English. For the romanization of Greek into other languages, see the corresponding articles in our sister wikis, such as "Romanisation du grec" on the French Wikipedia. Note, however, that the ELOT, UN, and ISO formats for Modern Greek intend themselves as translingual and may be applied in any language using the Latin alphabet.