Apart from its use in writing the Greek language, in both its ancient and its modern forms, the Greek alphabet today also serves as a source of technical symbols and labels in many domains of mathematics, science, and other fields.

Among the vowel symbols, Modern Greek sound values reflect the radical simplification of the vowel system of post-classical Greek, merging multiple formerly distinct vowel phonemes into a much smaller number. This leads to several groups of vowel letters denoting identical sounds today. Modern Greek orthography remains true to the historical spellings in most of these cases. As a consequence, the spellings of words in Modern Greek are often not predictable from the pronunciation alone, while the reverse mapping, from spelling to pronunciation, is usually regular and predictable.

Modern Greek speakers typically use the same, modern symbol–sound mappings in reading Greek of all historical stages. In other countries, students of Ancient Greek may use a variety of conventional approximations of the historical sound system in pronouncing Ancient Greek.

In the cases of the three historical sibilant letters below, the correspondence between Phoenician and Ancient Greek is less clear, with apparent mismatches both in letter names and sound values. The early history of these letters (and the fourth sibilant letter, obsolete san) has been a matter of some debate. Here too, the changes in the pronunciation of the letter names between Ancient and Modern Greek are regular.

Like Latin and other alphabetic scripts, Greek originally had only a single form of each letter, without a distinction between uppercase and lowercase. This distinction is an innovation of the modern era, drawing on different lines of development of the letter shapes in earlier handwriting.

On the other hand, the following phonetic letters have Unicode representations separate from their Greek alphabetic use, either because their conventional typographic shape is too different from the original, or because they also have secondary uses as regular alphabetic characters in some Latin-based alphabets, including separate Latin uppercase letters distinct from the Greek ones.

For computer usage, a variety of encodings have been used for Greek online, many of them documented in RFC .

For the range A0–FF (hex), it follows the Unicode range 370–3CF (see below) except that some symbols, like ©, ½, § etc. are used where Unicode has unused locations. Like all ISO-8859 encodings, it is equal to ASCII for 00–7F (hex).

This block also supports the Coptic alphabet. Formerly, most Coptic letters shared codepoints with similar-looking Greek letters; but in many scholarly works, both scripts occur, with quite different letter shapes, so as of Unicode 4.1, Coptic and Greek were disunified. Those Coptic letters with no Greek equivalents still remain in this block (U+03E2 to U+03EF).

To write polytonic Greek, one may use combining diacritical marks or the precomposed characters in the "Greek Extended" block (U+1F00 to U+1FFF).