Transliteration is the practice of transcribing a text in a writing system to a different writing system. For this purpose, the symbols in the origin writing system have to be mapped into the destination symbols. This process is generally based on phonetic similarities, although graphic similarities can also be taken. Transliteration must not be confused with transcription, which denotes the process of representing the sounds of one language into another.

The need for transliteration appears when a speaker of a language has to use different symbols to express his language, mainly due to unavailability of the original symbols. The clearest example is keyboards. When a Russian is abroad and wants to write in Cyrillic, he will find a different keyboard from the one that he is used to. The computer system may allow him activate Cyrillic script but, what if it does not? He will find himself with the need of writing Cyrillics with a western keyboard. The solution will be to express the Russian words with the closest equivalent Latin letter. Anyway, it is possible to find people who write Tchaikovsky, Tschaikowsky or Chaikovski. This is closer to a transcription. The objective is to find a neutral basis that does not look like transcription rather than transliteration.

At the beginning, this transliterations were done unofficially, but nowadays they are mostly standarized. Each government (whose official language uses a writing system different from the latin alphabet) has a set of rules to transliterate its alphabet, abjad, syllabary or ideographic system. This is also done in any context where the text is targeted at those who do not know the language: for example, for names on street signs, passports, and in dictionaries and textbooks for foreign learners of the language.

Transliteration is also extended to SMS and chats. This communication places are not always prepared to exchange non-Latin characters. For that reason, it is frequent to see transliteration in such environments.

The most common type of transliteration is Romanization, due to the situation of Latin (Roman) alphabet as standard. Here we can find Japanese transliteration, called Romaji. All Japanese who have attended elementary school since 1945 have been taught to read and write romanized Japanese. Romanization is also the most common system to input Japanese text into word processors and computers. Therefore, almost all Japanese are able to read and write Japanese using romaji. In this case of transliteration, one source symbol corresponds to set of output symbol (remember that Japanese uses syllabaries and ideograms).

In the case of Russian or Greek transliteration, every input symbol corresponds to one or two destination symbols. In this cases a chart of equivalences is enough to perform the transliteration. That's how we can read and understand Panathinaikos or Glasnost'. Pupils are also taught in school the Roman alphabet, so that they can find it easier when they have to learn a foreign language.