The basic Arabic alphabet contains 28 letters. Adaptations of the Arabic script for other languages added and removed some letters, as for Kurdish, Persian, Ottoman Turkish, Sindhi, Urdu, Malay, Pashto, and Malayalam (Arabi Malayalam), all of which have additional letters as shown below. There are no distinct upper and lower case letter forms.
Many letters look similar but are distinguished from one another by dots (i‘jām) above or below their central part (rasm). These dots are an integral part of a letter, since they distinguish between letters that represent different sounds. For example, the Arabic letters transliterated as b and t have the same basic shape, but b has one dot below, ب, and t has two dots above, ت.
Both printed and written Arabic are cursive, with most of the letters within a word directly connected to the adjacent letters.
There are two main collating sequences for the Arabic alphabet, abjad and hija.
The original abjadī order (أَبْجَدِي), used for lettering, derives from the order of the Phoenician alphabet, and is therefore similar to the order of other Phoenician-derived alphabets, such as the Hebrew alphabet. In this order, letters are also used as numbers, Abjad numerals, and possess the same alphanumeric code/cipher as Hebrew gematria and Greek isopsephy.
The hijā’ī (هِجَائِي) or alifbā’ī (أَلِفْبَائِي) order, used where lists of names and words are sorted, as in phonebooks, classroom lists, and dictionaries, groups letters by similarity of shape.
The abjadī order is not a simple historical continuation of the earlier north Semitic alphabetic order, since it has a position corresponding to the Aramaic letter samekh / semkat ס, yet no letter of the Arabic alphabet historically derives from that letter. Loss of sameḵ was compensated for by the split of shin ש into two independent Arabic letters, ش (shīn) and ﺱ (sīn) which moved up to take the place of sameḵ. The six other letters that do not correspond to any north Semitic letter are placed at the end.
This is commonly vocalized as follows:
- abjad hawwaz ḥuṭṭī kalaman sa‘faṣ qarashat thakhadh ḍaẓagh.
Another vocalization is:
- abujadin hawazin ḥuṭiya kalman sa‘faṣ qurishat thakhudh ḍaẓugh
This can be vocalized as:
- abujadin hawazin ḥuṭiya kalman ṣa‘faḍ qurisat thakhudh ẓaghush
Modern dictionaries and other reference books do not use the abjadī order to sort alphabetically; instead, the newer hijā’ī order is used wherein letters are partially grouped together by similarity of shape. The hijā’ī order is never used as numerals.