The orthography of the Greek language ultimately has its roots in the adoption of the Greek alphabet in the 9th century BC. Some time prior to that, one early form of Greek, Mycenaean, was written in Linear B, although there was a lapse of several centuries (the Greek Dark Ages) between the time Mycenaean stopped being written and the time when the Greek alphabet came into use.
Early Greek writing in the Greek alphabet was phonemic, different in each dialect. Since the adoption of the Ionic variant for Attic in 403 BC, however, Greek orthography has been largely conservative and historical.
This affects not only lexical items but also inflectional affixes, so correct orthography requires mastery of formal grammar, e.g. η καλή /i kaˈli/ 'the good one (fem. sing.)' vs. οι καλοί /i kaˈli/ 'the good ones (masc. pl.)'; καλώ /kaˈlo/ 'I call' vs. καλό /kaˈlo/ 'good (neut. sing.)'.
Similarly, the orthography preserves ancient doubled consonants, though these are now pronounced the same as single consonants, except in Cypriot Greek.
A digraph is a pair of letters used to write one sound or a combination of sounds that does not correspond to the written letters in sequence. The orthography of Greek includes several digraphs, including various pairs of vowel letters that used to be pronounced as diphthongs but have been shortened to monophthongs in pronunciation. Many of these are characteristic developments of modern Greek, but some were already present in Classical Greek. None of them is regarded as a letter of the alphabet.
The prohibitive hyphenation rules regarding vowel splitting are as follows:
All of the above rules are negative in that they indicate impermissible hyphen points within particular substrings of consecutive vowels.
Polytonic spelling uses a variety of diacritics to represent aspects of the pronunciation of ancient Greek. Polytonic, along with lowercase letters, became standard in Byzantine Greek, although the ancient distinctions had disappeared, replaced by a simple stress accent. The orthographies of modern Greek, both katharevousa and dhimotiki, used the polytonic system until 1982, when monotonic spelling was introduced. In some conservative contexts, such as the Church, polytonic spellings are still used.
Monotonic orthography, adopted in 1982, replaces the ancient diacritics with just two: the acute accent (tónos, e.g. ί), used to mark the stressed syllable in polysyllabic words, and the diaeresis (dialytiká, e.g. ϊ), which indicates that the vowel is not part of a digraph.
Ancient Greek was written as scripta continua without spacing or interpuncts. Over time, a variety of symbols appeared. A system of dots credited to Aristophanes of Byzantium was developed in the 3rd century BC: a low dot ⟨.⟩ marked an occasion for a short breath after a short phrase, a middot ⟨·⟩ marked an occasion for a longer breath after a longer passage, and a high dot ⟨˙⟩ marked a full stop at the end of a completed thought. Other writers employed two dot punctuation ⟨⁚⟩ to mark the ends of sentences or changing speakers. Less often, arrangements of three ⟨⁝⟩, four ⟨⁞ or ⁘⟩, and five dots ⟨⁙⟩ appeared. Such interline punctuation could be noted or replaced by a variety of paragraphoi, long marks which trailed between lines of text; these might also mark changes of speakers. Blank lines or various coronides marked the ends of sections. (A separate coronis was used to mark contractions; its early forms looked like an apostrophe between the two elided words.) Over time, the main punctuation came to be a full stop marked by a single dot at varying heights, a partial stop marked by various forms of commas, and the hypodiastole ⟨⸒⟩ and papyrological hyphen ⟨‿⟩ or ⟨ ͜ ⟩. These served to show whether an ambiguous series of letters should be read as (respectively) a single word or as a pair of words. Later Aristarchus of Samothrace modified this system (see: Aristarchian symbols).
Following the advent of printing, most Greek punctuation was gradually standardized with French: the hypodiastole was fully unified with the comma, the comma serves as the decimal point (and in this use is called the hypodiastole) and it also functions as a silent letter in a handful of Greek words, principally distinguishing ό,τι (ó,ti, "whatever") from ότι (óti, "that"). The full stop serves as the thousands separator, and guillemets (εισαγωγικά isagoyika) and em-length quotation dashes (παύλα pavla) typically serve to indicate direct speech. When quotations are nested, double and then single quotation marks are used: ⟨«…“…‘…’…”…»⟩. The right-pointing double Guillemets (ομειωματικά omiomatiká) ⟨»⟩ serve as Ditto mark. The principal difference is the Greek question mark ⟨;⟩, which developed a shape so similar to the Latinate semicolon ⟨;⟩ that Unicode decomposes its separate code point identically. The ano teleia middot serves as the Greek semicolon but is so uncommon that it has often been left off of Greek keyboards. The exclamation mark (θαυμαστικό thavmastikó) is mostly used as in English. The hyphen, the brackets, the colon, the ellipsis and the slash are also in use. The slash has the additional function of forming common abbreviations like α/φοί for αδελφοί 'brothers'. The ligature kai (ϗ) is sometimes used for the same function as the English ampersand.
There are special rules for how to write Greek numerals. In modern Greek, a number of changes have been made. Instead of extending an overline over an entire number (like χξϛ), a keraia (κεραία, lit. "hornlike projection") is placed to its upper right, a development of the short marks formerly used for single numbers and fractions. The modern keraia is a symbol (ʹ) similar to the acute accent (´), but has its own Unicode character, encoded as U+0374. Alexander the Great's father Philip II of Macedon is thus known as Φίλιππος Βʹ in modern Greek. A lower left keraia (Unicode: U+0375, "Greek Lower Numeral Sign") is now standard for identifying thousands: 2015 is represented as ͵ΒΙΕʹ (2000 + 10 + 5).