The Khmer script (អក្ខរក្រមខេមរភាសា; âkkhârâkrâm khémârâ phéasa, informally aksar Khmer; អក្សរខ្មែរ) is used to write the Khmer language which is the official language of Cambodia. It is often considered to be the longest alphabet in the world.

It is generally thought that the Khmer script developed from the Pallava script of India. The oldest dated inscription in Khmer was found at Angkor Borei in Takev Province south of Phnom Penh and dates from 611 AD.
Those inscriptions that have survived are engraved in stone and the evolution of Khmer script is as follows:

• Han Chey, approximately 6th century

• Veal Kan Teng, end of the 6th or early 7th century

• Ang Chomney Kor, 667 century

• Inn Kor Sey, 970 century

• Preash Keo, 1002 AD

• Nor Korr, 1066 AD

• Banteay Chmar, early 12th or 13th century

• Angkor Wat, 13th century

• Angkor script, 1702 AD

The Khmer alphabet has fewer symbols for vowels than the language has vowel phonemes. To account for this, each consonant belongs to one of two series, and the vowel produced depends on which series the consonant belongs to (making it an abugida rather than a true alphabet). Therefore, most vowel signs have two possible pronunciations, depending on which series the consonant belongs to. When no vowel sign is present, usually the inherent vowel of the consonant is used. Vowels signs can be divided into two groups: dependent vowel signs, which are written around a consonant letter, and independent vowel letters, which can stand alone. Dependent vowel signs are used more frequently than independent vowels and all independent vowel letters can be phonetically rendered with a dependent vowel. Khmer also has a number of diacritics, which can change the series of the consonant or change the pronunciation of the vowel.

Styles

There are several styles of Khmer script which are used for different purposes.

• 'Âksâr chriĕng' refers to slanted (or italic) letters. Slanted letters do not serve the same purpose as italics in English, so entire bodies of text such as novels and other publications may be produced in 'âksâr chriĕng' .

• 'Âksâr chhôr' refers to any style that is "standing" or upright. Upright letters were previously not as common as 'âksâr chriĕng', but now most computer fonts display Khmer text upright by default for ease of reading.

• 'Âksâr mul' is a round style which is used for titles and headings in Cambodian documents, books, or currency, on shop signs or banners. Religious text on palm leaves may be entirely written in this script style. It is sometimes used to write royal names while the surrounding text remains plain. Several consonants and some subscripts in this style take on different forms than their counterparts in the standard orthography.

• 'Âksâr khâm' is a variation of 'âksâr mul', with only minor differences. See also Khom script.

The last two styles, when handwritten, are usually pencil-line width, however, in printed form and on computer fonts, they are usually seen in wider widths. Most Khmer computer fonts depict neither style correctly; in fact, some may meld elements of 'âksâr mul' and 'âksâr khâm' into one style, so generally either is referred to as 'âksâr mul'.

Consonants

There are 35 Khmer consonants symbols, although modern Khmer only uses 33, two having become obsolete. Subscript consonants are special forms used to form consonant clusters. Also sometimes referred to as "sub-consonants", subscript consonants often resemble the corresponding consonant symbol, only smaller. In Khmer, they are known as 'cheung âksâr' (ជើង​អក្សរ), meaning the foot of a letter. In forming consonant clusters, the second (and where necessary, the third) consonant sound of the cluster is written as a subscript which cancels the inherent vowel of the preceding consonant. Most subscript consonants are written directly below the consonant which they follow, although subscript /r/ is written before while a few others have ascending elements which appear after.

Listed in the table below are the pronunciations of the consonants when recited. Although Khmer spelling is very regular, the pronunciation of some consonants may be slightly different from the recited version in a few words. This is especially true in loan words. The IPA values given are for consonants in the initial or medial position. Because of Khmer phonology, in which final stops are unreleased and possible finals are limited, word-final values may differ. For example, word-final /s/ is pronounced /h/ and, in most dialects, word-final /r/ is silent. The inherent vowels of consonants in the final position are almost never pronounced. The two obsolete consonants are highlighted in gray.

* The subscript for the consonant lâ is included in Unicode although its usage in modern Khmer is generally non-existent.

For some phonemes in loanwords, the Khmer writing system has 'created' supplementary consonants. Most of these consonants are created by stacking a subscript under the character for to form digraphs. The consonant for , however, is created by using the diacritical sign called musĕkâtônd over the consonant for . These additional consonants are mainly used to represent sounds in French and Thai loanwords.

Dependent vowels

There are 16 unique dependent vowel symbols, although this name can be added up to 24 when dependent vowels with diacritical symbols are included. Dependent vowels are known in Khmer as srăk nissăy (ស្រៈនិស្ស័យ) or srăk phsâm (ស្រៈផ្សំ). Dependent vowels must always be combined with a consonant in orthography. For most of the vowel symbols, there are two sounds (registers). The sound of the vowel used depends on the series (the inherent vowel) of the dominant consonant in a syllable cluster.

• For technical reasons, the dependent vowels are seen here paired with the letter អ (KHMER LETTER QA in Unicode) as not all browsers will display them by themselves correctly.

Independent vowels

Independent vowels are vowels that do not have to be paired with a consonant in a syllable, hence the name. In Khmer they are called srăk penhtuŏ (ស្រៈពេញតួ) which means complete vowels.

Diacritics

Punctuation marks

The Khmer script uses several unique punctuation marks as well as some borrowed from the Latin script such as the question mark. The period in the Khmer language "។" resembles an eighth rest in music writing.

Ligatures

Most consonants, including a few of the subscripts, form ligatures with all dependent vowels that contain the symbol used for the vowel a (ា). A lot of these ligatures are easily recognizable, however a few may not be. One of the more unrecognizable is the ligature for the bâ and a which was created to differentiate it from the consonant symbol hâ as well as the ligature for châ and a. It is not always necessary to connect consonants with the dependent vowel a.

Examples of ligatured symbols:
Ligatured consonant subscript and vowel combination:

Numerals

The numerals of the Khmer script, similar to that used by other civilizations in Southeast Asia, are also derived from the southern Indian script. Arabic numerals are also used, but to a lesser extent.

Khmer in Unicode

The Unicode range for Khmer consists of two ranges: U+1780 ... U+17FF for the basic characters, and U+19E0 - U+19FF for additional symbols. Grey areas indicate non-assigned code points.