Wylie is a method to transliterate the Tibetan script into Roman script. This transliteration method was refined in 1959 by Turrell Wylie and has subsequently become a standard transliteration scheme in Tibetan studies, especially in the Western world.
Turrel Wylie's original publication can be found here.
Any Tibetan language transliteration method can either seek to accurately reproduce the pronunciation of spoken Tibetan, or to reproduce the spelling of written Tibetan. The two differ widely as Tibetan orthography became fixed in the 11th century, while pronunciation continued to evolve. Wylie does not try to give pronunciation hints and serves only to accurately reproduce written Tibetan.
The original proposal for Wylie did not define how to transliterate Sanskrit transliterations into Tibetan often found within Mantras. This was addressed by a proposal for the Extended Wylie Transliteration System proposed by the THDL project of the University Virginia.
Extended Wylie (EWTS) is todays de-facto standard for computer software working with wylie. The specification for EWTS can be found here:
A good introduction into Wylie is found here:
See the Bodhichitta article for an example of Wylie-encoded Tibetan.
Text adapted for wikipedia.org: