The Tai Yo script is used to write the Tai Yo language (also called Yoy, Tai Do, Tay Muoi, Tay Quy Chau, or Tay-Jo) spoken in Laos, Thailand and Vietnam. It is not believed to be in current use, having been replaced by the Latin script.

The script is written vertically, from top to bottom and from right to left. Books written in the script accordingly open on the left.

There are three types of consonant symbol in Tai Yo. Twenty-four symbols are used only at the start of a syllable. Five symbols are used only at the end of a syllable. Three symbols can be used either at the start or at the end of a syllable, although their position in the syllable dictates their pronunciation. At the start they represent [ɓ], [ƌ], [ɲ], but at the end they represent [p], [t], [j].

There is a tone mark for indicating tone.

Consonants do not contain an inherent vowel; all vowels are written explicitly by means of dependent symbols. There are 15 vowel symbols in total, 5 of which represent diphthongs. Vowels can be joined after (that is, below) a consonant, or to the right of it.

There are 5 (possibly 6) consonant+vowel ligatures, representing at, ak, am, an, ang, (ap).

One symbol can represent either one of a number of vowels, or the labialization of a consonant. When written below the consonant it represents the dipthong [ie] or [ia]; when it is both written to the right of the consonant and is syllable-final it represents [ăi]; when it is both written to the right and is followed by a vowel it represents labialization. The exception to representing labialization with this symbol is [kw], which is written with a separate symbol.

This script is not currently recognized by  ISO 15924, but is included in ScriptSource for research purposes. If you have any information on this script, please add the information to the site. Your contributions can be a great help in refining and expanding the ISO 15924 standard.