In The Unicode Standard, Thai script implementation is discussed in  Chapter 16 Southeast Asia.

The Thai script was encoded in The Unicode Standard version 1.0. The script is encoded in the following block:

BlocksCharacter RangeAdded in Unicode VersionUnicode Chart
Thai 0E00..0E7F 1.0  U0E00.pdf

A number of proposals for its inclusion have been submitted to the Unicode Technical Committee and WG2:

1999-04-29 ISO/IEC 14651 (informative annex) Thai String Collation — Theppitak Karoonboonyanan ( L2/99-136)

2001-03-16 N2332 - Thai Character Names in FDIS 8859-11 — Surayuth Boonmatat ( WG2 N2332,  L2/01-122)

2001-03-16 Change of Thai Names requested (8859-11) — Michael Everson ( L2/01-120)

2001-03-16 FDIS 8859-11 – Thai — Johan van Wingen ( L2/01-121)

2001-07-02 Revised Text of FCD 8859-11, Information technology — 8-bit single-byte coded graphic character sets — Part 11: Latin/Thai alphabet — Johan van Wingen, Surayuth Boonmatat ( L2/01-289)

2002-01-14 Character Properties for avagrahas, etc. — Kenneth Whistler ( L2/02-017)

2002-01-14 Character Properties for repetition marks — Kenneth Whistler ( L2/02-016)

2003-06-12 Thai and Lao collation weighting rules — Kent Karlsson ( L2/03-185)

2004-03-09 Ordering rules for Khmer, Thai, and Lao; CTT suggestion — Kent Karlsson ( WG2 N2717.doc,  L2/04-110)

2004-03-09 Ordering rules for Khmer, Thai, and Lao; suggestions for annex C.2 changes and a new annex B.5 — Kent Karlsson ( WG2 N2718.doc,  L2/04-111)

2004-07-18 Two problems in Thai rendering — Eric Muller ( L2/04-332)

2006-03-06 Thai collation errors — James Clark ( L2/06-082)

2006-07-27 Re: document Sk vs Lm vs — Martin Hosken ( L2/06-243)

2009-08-03 Grapheme break changes, especially for Thai and Lao — Peter Edberg ( L2/09-265)

2010-09-17 Proposal to change UAX#29 in response to Thai, Lao, Tai Dam user needs — Martin Hosken ( L2/10-460)

2010-11-01 Proposal not to encode 4 minority Thai letters for Patani Malay — Martin Hosken ( L2/10-451)

2011-02-03 Response to UTC Suggestions Regarding Thai in UAX#29 — Martin Hosken ( L2/11-051)

2011-04-18 Proposal to change grapheme extending properties of various characters — Martin Hosken ( L2/11-114)

2012-01-26 Grapheme-break related properties for U+0E2F THAI CHARACTER PAIYANNOI' — Nattapong Siralappanich, V S Umamaheswaran ( L2/12-038)