The Lao script is a syllabic alphabet, or abugida, that is employed to write the Lao language. Like other Southeast Asian scripts, its deep origin lies in Indian scripts, most remotely the Brahmi script and later the Pallava script of Southern India. The actual origin of the Lao script is somewhat more obscure. It is likely influenced by Khmer, which is considered to be the oldest script in Southeast Asia. The Lao script also shares a lot of similarity with the Thai script, and there was a lot of coevolution between the scripts considering their geographic proximity and linguistic afinity (the Lao language belongs to the Tai family of languages and is a relative of the Thai language).
The following is the basic signs of the Lao script.
Due to phonetic changes in the Lao language through history, a good number of Lao letters came to represent two sounds, one at the start of a syllable an the other at the end. For example, is pronounced [kh] at the beginning of a syllable and [k] at the end. This is represented in the chart as kh- for the syllable-initial value and -k for the syllable-ending value.
Another distinctive feature of the Lao script is that individual letters belong to one of three classes, conveniently termed class 1, 2, and 3. These classes dictate how tones are represented (which you will see below).
Indication of vowels in the Lao script is achieved through the use of extra strokes called vowel diacritics that are attached to the basic letter. Some vowels are actually represented by multiple vowel diacritics. The Lao language has nine vowels, namely [i], [ɯ], [u], [e], [ɤ], [o], [æ], [a], and [ɔ]. Vowels can also be short, long, or combined into a number of diphthongs. As a consequence, the number of vowel diacritic combinations are quite large, as illustrated in the following chart.
An interesting note is that some of the vowels have two vowel diacritics. One variant is used when the vowel is between consonants whereas the other form is used in all other positions. For example, the syllable /ke/ can be written as when it is followed by a consonant (transcribed as ke-), and as when it is at the end of a syllable (transcribed as ke).
Traditionally in Brahmi-derived abugida scripts, a sign is in fact a syllable containing a consonant sound and an inherent vowel, [ɤ] in the case of Lao. While Lao still retains this feature, the [ɤ] sound is always indicated by an actual vowel diacritic. In other words, Lao signs can be considered to be purely consonant letters, with vowel indication using means of extra strokes exclusively.
The Lao language is a tonal language, meaning that two words with the same sound but different tones have different meanings. There are six tones in Lao, which are high, high falling, mid, low falling, low rising, and low. The representation of tones in the Lao script follows complex rules. As mentioned earlier, the class of the letter is one of the factors in indicating tone. Another factor is whether a syllable is open (ending in a long vowel or nasal consonants) or closed (ending in stop consonants or a short vowel followed by glottal stop). There are also four tone marks used in conjunction with open syllables to indicate tones too, although only two are used widely. And finally, the vowel length in a closed syllable is another variable in determining the tone.
The complex "matrix" of tones is best explained in the following grid.
Unlike Western or even Indian scripts, words in Lao are not separated by space or a special mark, but are instead joined together. Spaces are used only at an end of sentences and paragraphs.