The Greek and Coptic block — U+0370 through U+03FF, 135 codepoints assigned in a 144-position window — houses the most influential alphabet in European intellectual history, and the script you have probably read more often than you realize. Every physics textbook, mathematics paper, statistical formula, and corporate logo uses Greek letters somewhere. The modern Greek alphabet has 24 letters; Unicode encodes each in both upper and lower case, plus accented forms for polytonic text, plus a small set of archaic letters revived for numbering and mathematics.
About this block
The block was present from Unicode 1.0 in 1991. It corresponds closely to ISO 8859-7, the legacy eight-bit codepage for modern Greek, with extensions for the polytonic accents needed by ancient and ecclesiastical texts. Uppercase Greek occupies U+0391–U+03A9 (Α Β Γ Δ Ε Ζ Η Θ Ι Κ Λ Μ Ν Ξ Ο Π Ρ Σ Τ Υ Φ Χ Ψ Ω) — with one reserved position at U+03A2 where the obsolete final-sigma capital would have gone. Lowercase Greek runs U+03B1–U+03C9 (α β γ δ ε ζ η θ ι κ λ μ ν ξ ο π ρ ς σ τ υ φ χ ψ ω), with both lowercase sigma forms: σ (medial, U+03C3) used inside or at the start of words, and ς (final, U+03C2) used at the end. This is the same distinction every Greek reader makes automatically, and the only major case-insensitive complication when normalizing Greek text.
Before the main alphabet, the block places diacritics, archaic letters, and combining marks. U+0374 ʹ NUMERAL SIGN and U+0375 ͵ LOWER NUMERAL SIGN are the two marks used in the Greek-letter numeral system (where α′ = 1, β′ = 2, and so on). U+0376/U+0377 are Pamphylian digamma forms. U+037A YPOGEGRAMMENI is the modern iota subscript. U+0384 tonos and U+0385 dialytika tonos are the modern Greek accent marks; U+0386–U+038F hold the precomposed accented capitals (Ά Έ Ή Ί Ό Ύ Ώ). The archaic letters digamma ϝ (U+03DC capital, U+03DD small), koppa ϟ (U+03DE/U+03DF), and sampi ϡ (U+03E0/U+03E1) were preserved primarily because they represent specific numeric values (6, 90, and 900) in the Greek numeral system.
The block was originally called simply "Greek." It picked up "and Coptic" because Coptic — the Christian liturgical script of Egypt, descended from Greek and written in many of the same letterforms — was unified with Greek in early Unicode for historic and pragmatic reasons. Letters like Coptic shei ϣ, fai ϥ, hori ϧ, gangia ϫ, shima ϭ, and dei ϯ were placed alongside Greek archaic letters because typesetting conventions had often treated them as variants. Unicode 4.1 (2005) reversed this decision: a dedicated Coptic block was added at U+2C80–U+2CFF, and the formerly-shared Coptic letters in the Greek and Coptic block were kept for compatibility but flagged as "decomposed Coptic" — modern Coptic text should use the dedicated block instead.
Outside its linguistic role, Greek is the working alphabet of mathematics and science. π, λ, μ, σ, Σ, Δ, Φ, Ψ, Ω, and θ are used so frequently in mathematical notation that Unicode also provides them as math italics in the Mathematical Alphanumeric Symbols block (U+1D6A8–U+1D7CB), guaranteeing the right font for mathematical rendering even when Greek-language Greek would render the wrong way.