A heptagraph (from the Greek: επτά, heptá, "seven" and γράφω, gráphō, "write") is a sequence of seven letters used to represent a single sound (phoneme), or a combination of sounds, that do not correspond to the individual values of the letters.

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Heptagraphs are extremely rare. Most other fixed sequences of seven letters are composed of shorter multigraphs with a predictable result. The seven-letter German sequence ⟨schtsch⟩, used to transliterate the Russian and Ukrainian letter ⟨щ⟩, as in ⟨Borschtsch⟩ [bɔʁʃt͡ʃ] for Russian/Ukrainian ⟨борщ⟩ (Russian: [borɕː], Ukrainian: [bɔrʃt͡ʃ]) "borscht", is a sequence of a trigraph ⟨sch⟩ [ʃ] and a tetragraph ⟨tsch⟩ [t͡ʃ]. Likewise, the Juu languages have been claimed to have a heptagraph ⟨dtsʼkxʼ⟩, but this is also a sequence, of ⟨dtsʼ⟩ and ⟨kxʼ⟩.

• Multigraph (orthography)
• Digraph (orthography)
• Pentagraph
• Hexagraph