Greek orthography has used a variety of diacritics starting in the Hellenistic period. The complex polytonic orthography which notated Ancient Greek phonology was used until 1982, when it was supplanted by the simplified monotonic orthography, which corresponds to Modern Greek phonology, and requires only two diacritics.

In the polytonic system, the acute accent ( ´ ), the grave accent ( ` ), and the circumflex ( ˆ ) indicate different kinds of pitch accents. The rough breathing ( ῾ ) indicates aspiration (the presence of an /h/ sound), while the smooth breathing ( ᾿ ) indicates a lack of aspiration. It is said[by whom?] to have been introduced by Aristophanes of Byzantium around 200 BC, and was the standard orthography for all varieties of Greek from Hellenistic times until 1982, although the distinctions it represented had disappeared from the spoken language early in the Christian era. Since the pitch accent eventually gave place to a dynamic accent, and aspiration was lost in Greek, most polytonic diacritics have no phonetic significance in modern usage, and merely serve to reveal the underlying ancient Greek etymology.

The monotonic orthography (μονός "single", τόνος "accent") is the simplified spelling introduced in 1982 for modern Greek, resembling the diacritics used in Spanish. It replaced all accent marks with just one, the acute, and abandoned the use of the breathings. The diaeresis ( ¨ ) remained in use to indicate a hiatus: compare modern Greek παϊδάκια [paiðaca] (lamb chops) and παιδάκια [peðaca] (little children). The traditional system is called polytonic orthography to distinguish it from the monotonic one.