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In a right-to-left, top-to-bottom script (commonly shortened to right to left or abbreviated RTL), writing starts from the right of the page and continues to the left, proceeding from top to bottom for new lines. This can be contrasted against left-to-right writing systems, where writing starts from the left of the page and continues to the right.
Right-to-left can also refer to top-to-bottom, right-to-left (TB-RL or TBRL) scripts such as Chinese, Japanese, and Korean, though in modern times they are also commonly written left to right. Books designed for predominately TBRL vertical text open in the same direction as those for RTL horizontal text: the spine is on the right and pages are numbered from right-to-left.
Arabic, Hebrew, Persian, and Urdu are the most widespread RTL writing systems in modern times. As usage of the Arabic script spread, the repertoire of 28 characters used to write the Arabic language was supplemented to accommodate the sounds of many other languages such as Persian, Pashto, etc. While the Hebrew alphabet is used to write the Hebrew language, it is also used to write other Jewish languages such as Yiddish and Judaeo-Spanish.
Syriac and Mandaean (Mandaic) scripts are derived from Aramaic and are written RTL. Samaritan is similar, but developed from Proto-Hebrew rather than Aramaic. Many other ancient and historic scripts derived from Aramaic inherited its right-to-left direction.
Several languages have both Arabic RTL and non-Arabic LTR writing systems. For example, Sindhi is commonly written in Arabic and Devanagari scripts, and a number of others have been used. Kurdish may be written in Arabic, Latin, Cyrillic or Armenian script.
Ancient examples of text using alphabets such as Phoenician, Greek, or Old Italic may exist variously in left-to-right, right-to-left, or boustrophedon order; therefore, it is not always possible to classify some ancient writing systems as purely RTL or LTR.
Right-to-left, top-to-bottom text is supported in common computer software. Often, this support must be explicitly enabled. Right-to-left text can be mixed with left-to-right text in bi-directional text.
List of RTL scripts
Examples of right-to-left scripts (with ISO 15924 codes in brackets) are:
- Arabic script (Arab 160, Aran 161) – used for Arabic, Persian, Urdu and many other languages.
- Hebrew alphabet (Hebr 125) – used for Hebrew, Yiddish and some other Jewish languages.
- Thaana (Thaa 170) – used for Dhivehi.
- Syriac alphabet (Syrc 135, variants 136–138 Syrn, Syrj, Syre) – used for varieties of the Syriac language.
- Mandaic alphabet (Mand 140) – closely related to Syriac, used for the Mandaic language.
- Samaritan alphabet (Samr 123) – closely related to Hebrew, used for the Samaritans' writings.
- Mende Kikakui (Mend 438) – for Mende in Sierra Leone. Devised by Mohammed Turay and Kisimi Kamara in the late 19th century. Still used but only by about 500 people.
- N'Ko script (Nkoo 165) – devised in 1949 for the Manding languages of West Africa.
- Garay alphabet – designed in 1961 for the Wolof language
- Adlam (Adlm 166) – devised in the 1980s for writing the Fula languages of West and Central Africa.
- Hanifi Rohingya (Rohg 167) – developed in the 1980s for the Rohingya language.
- Indus script
- Cypriot syllabary (Cprt 403) – predates Phoenician influence.
- Phoenician alphabet (Phnx 115) – ancient, precursor to Hebrew, Imperial Aramaic, and Greek.
- Imperial Aramaic alphabet (Armi 124) – ancient, closely related to Hebrew and Phoenician. Spread widely by the Neo-Assyrian and Achaemenid empires. The later Palmyrene form (Palm 126) was also used to write Aramaic.
- Old South Arabian (Sarb)
- Old North Arabian (Narb)
- Pahlavi scripts (130–133: Prti, Phli, Phlp, Phlv) – derived from Aramaic.
- Avestan alphabet (Avst 134) – from Pahlavi, with added letters. Used for recording the Zoroastrian sacred texts during the Sassanid era.
- Hatran alphabet (Hatr 127), used to write the Aramaic of Hatra
- Sogdian (no code), and Manichaean (Mani 139, associated with the Manichaean religion) – derived from Syriac. Sogdian eventually rotated from RTL to top-to-bottom, giving rise to the Old Uyghur, Mongolian, and Manchu vertical scripts.
- Nabatean alphabet (Nbat) – intermediate between Syriac and Arabic.
- Kharosthi (Khar 305) – an ancient script of India, derived from Aramaic.
- Old Turkic runes (also called Orkhon runes Orkh 175)
- Old Hungarian runes (Hung 176).
- Old Italic alphabets (Ital 210) – Early Etruscan was RTL but LTR examples later became more common. Umbrian, Oscan, and Faliscan were written right-to-left. Unicode treats Old Italic as left-to-right, to match modern usage. Some texts are boustrophedon 
- Lydian alphabet (Lydi 116) – ancient; some texts are left-to-right or boustrophedon.
- "Introduction to typing and using RTL (Right to Left) text, and configuring software applications to support RTL".
- Davis, Mark; Everson, Michael; Freytag, Asmus; Jenkins, John H. (2001-05-16). "Unicode Standard Annex #27: Unicode 3.1".
Most early Etruscan texts have right-to-left directionality. From the third century BCE, left-to-right texts appear, showing the influence of Latin. Oscan, Umbrian, and Faliscan also generally have right-to-left directionality. Boustrophedon appears rarely, and not especially early .... Despite this, for reasons of implementation simplicity, many scholars prefer left-to-right presentation of texts, as this is also their practice when transcribing the texts into Latin script. Accordingly, the Old Italic script has a default directionality of strong left-to-right in this standard. When directional overrides are used to produce right-to-left presentation, the glyphs in fonts must be mirrored ...