Phonetic and phonemic transcription is usually represented by means of the symbols of the International Phonetic Alphabet (IPA). The IPA was revised at the Kiel Convention in 1989 and the most recently revised version has appeared in 1993 (IPA, 1993) (also available at URL http://www.arts.gla.ac. uk/IPA/ipachart.html). The principles on which the IPA is based can be found in the report on the Kiel Convention published in the Journal of the International Phonetic Association (IPA, 1989). Illustrations of the application of the systems with sample transcriptions for several languages regularly appear in the same Journal, and recordings showing the pronunciation of each of the sounds are also available (Wells - House, 1995). The International Phonetic Association has its home page at URL http://www.arts.gla.ac.uk/ IPA/ipa.html.
The International Phonetic Alphabet is not only the most common transcription system used in linguistic research, but is also the standard for representing phonemic and phonetic information recommended by NERC and by the TEI.
However, different traditions have developed different phonetic alphabets more adapted to their respective needs, such as the current American system arising from work in the transcription of American-Indian languages, the system used by European romance philologists engaged in diachronic and dialectological research or the conventions used for scholars working with African, Slavonic or Indian languages. Specific phonetic alphabets are sometimes linked to national traditions, arising from the needs to have an accurate narrow transcription of a specific language. A useful guide to phonetic symbols has been published by Pullum & Ladusaw (1986), where different symbols and usages are explained.
Extensions of the IPA have been also developed for special purposes, in particular for the transcription of disordered speech. The conventions proposed by Ball and his collaborators (Duckworth et al., 1993; Ball et al., 1994; Ball et al., 1996) have been adopted by Clinical Linguistics & Phonetics, the official journal of ICPLA, the International Clinical Phonetics and Linguistic Association (the association has its home page at URL http://tpowel.comdis.lsumc.edu/icpla/icpla.htm).