Although commonly referred to as the Thai alphabet, the script is not a true alphabet but an abugida, a writing system in which the full characters represent consonants with diacritical marks for vowels; the absence of a vowel diacritic gives an implied 'a' or 'o'.

[1] The earliest attestation of the Thai script is the Ram Khamhaeng Inscription dated to 1292, however some scholars question its authenticity.

[2] Finally, the script wrote vowel marks on the main line, however this innovation fell out of use not long after.

A bird's eye ๏ (Thai: ตาไก่, ta kai, officially called ฟองมัน, fong man) formerly indicated paragraphs.

Thai (along with its sister system, Lao) lacks conjunct consonants and independent vowels, while both designs are common among Brahmic scripts (e.g., Burmese and Balinese).

These class designations reflect phonetic qualities of the sounds to which the letters originally corresponded in Old Thai.

[nb 1] Today, the class of a consonant without a tone mark, along with the short or long length of the accompanying vowel, determine the base accent (พื้นเสียง, phuen siang).

[nb 2] To aid learning, each consonant is traditionally associated with an acrophonic Thai word that either starts with the same sound, or features it prominently.

When the first Thai typewriter was developed by Edwin Hunter McFarland in 1892, there was simply no space for all characters, thus two had to be left out.

The entries in columns initial and final indicate the pronunciation for that consonant in the corresponding positions in a syllable.

Although official standards for romanisation are the Royal Thai General System of Transcription (RTGS) defined by the Royal Thai Institute, and the almost identical ISO 11940-2 defined by the International Organization for Standardization, many publications use different romanisation systems.

Thai distinguishes among three voice/aspiration patterns for plosive consonants: Where English has only a distinction between the voiced, unaspirated /b/ and the unvoiced, aspirated /pʰ/, Thai distinguishes a third sound which is neither voiced nor aspirated, which occurs in English only as an allophone of /p/, approximately the sound of the p in "spin".

Among these consonants, excluding the disused ฃ and ฅ, six (ฉ, ผ, ฝ, ห, อ, ฮ) cannot be used as a final.

The first symbol 'ฤ' is common in many Sanskrit and Pali words and 'ฤๅ' less so, but does occur as the primary spelling for the Thai adaptation of Sanskrit 'rishi' and treu (Thai: ตฤๅ /trɯ̄ː/ or /trīː/), a very rare Khmer loan word for 'fish' only found in ancient poetry.

As alphabetical entries, ฤ ฤๅ follow ร, and themselves can be read as a combination of consonant and vowel, equivalent to รึ (short), and รือ (long) (and the obsolete pair as ลึ, ลือ), respectively.

Moreover, ฤ can act as ริ as an integral part in many words mostly borrowed from Sanskrit such as กฤษณะ (kritsana, not kruetsana), ฤทธิ์ (rit, not ruet), and กฤษดา (kritsada, not kruetsada), for example.

In the past, prior to the turn of the twentieth century, it was common for writers to substitute these letters in native vocabulary that contained similar sounds as a shorthand that was acceptable in writing at the time.

Tones are realised in the vowels, but indicated in the script by a combination of the class of the initial consonant (high, mid or low), vowel length (long or short), closing consonant (plosive or sonorant, called dead or live) and, if present, one of four tone marks, whose names derive from the names of the digits 1–4 borrowed from Pali or Sanskrit.

Some of the characters can mark the beginning or end of a sentence, chapter, or episode of a story or of a stanza in a poem.

ค, ฅ, ฆ ฎ, ฏ, ฐ, ฑ, ฒ, ด, ต, ถ, ท, ธ, ศ, ษ, ส พ, ฟ, ภ colour codes red: dead green: alive colour codes pink: long vowel, shortened by add "ะ"(no ending consonant) or "-็"(with ending consonant) green: long vowel, has a special form when shortened The Thai script (like all Indic scripts) uses a number of modifications to write Sanskrit and related languages (in particular, Pali).

This is an example of a Pali text written using the Thai Sanskrit orthography: อรหํ สมฺมาสมฺพุทฺโธ ภควา [arahaṃ sammāsambuddho bhagavā].

This disjoint between transcription and spoken value explains the romanisation for Sanskrit names in Thailand that many foreigners find confusing.

Plosives (also called stops) are listed in their traditional Sanskrit order, which corresponds to Thai alphabetical order from ก to ม with three exceptions: in Thai, high-class ข is followed by two obsolete characters with no Sanskrit equivalent, high-class ฃ and low-class ฅ; low-class ช is followed by sibilant ซ (low-class equivalent of high-class sibilant ส that follows ศ and ษ.)

[ka] /k/ [kha] /kʰ/ [ga] /g/ [gha] /gʱ/ [ṅa] /ŋ/ [ca] /c/, /tɕ/ [cha] /cʰ/, /tɕʰ/ [ja] /ɟ/, /d͡ʑ/ [jha] /ɟʱ/, /d͡ʑʱ/ [ña] /ɲ/ ट[ṭa] /ʈ/ ठ[ṭha] /ʈʰ/ ड[ḍa] /ɖ/ ढ[ḍha] /ɖʱ/ ण[ṇa] /ɳ/ त[ta] /t/ थ[tha] /tʰ/ द[da] /d/ ध[dha] /dʱ/ न[na] /n/ प[pa] /p/ फ[pha] /pʰ/ ब[ba] /b/ भ[bha] /bʱ/ म[ma] /m/ None of the Sanskrit plosives are pronounced as the Thai voiced plosives, so these are not represented in the table.

So, while there is a clear distinction between ช and ฌ in Sanskrit, in Thai these two consonants are pronounced identically (including tone).

In modern Thai, the distinction between the three high-class consonants has been lost and all three are pronounced 'sà'; however, foreign words with a sh-sound may still be transcribed as if the Sanskrit values still hold (e.g., ang-grit อังกฤษ for English instead of อังกฤส).

(A popular beer is romanized as Singha, but in Thai is สิงห์, with a karan on the ห; correct pronunciation is "sing", but foreigners to Thailand typically say "sing-ha".)

อฺ Because the Thai script is an abugida, a symbol (equivalent to virāma in devanagari) needs to be added to indicate that the implied vowel is not to be pronounced.

หญ ญ ช Thai script was added to the Unicode Standard in October 1991 with the release of version 1.0.

It is a verbatim copy of the older TIS-620 character set which encodes the vowels เ, แ, โ, ใ and ไ before the consonants they follow, and thus Thai, Lao, Tai Viet and New Tai Lue are the only Brahmic scripts in Unicode that use visual order instead of logical order.