A lipogram (from Ancient Greek: λειπογράμματος, leipográmmatos, "leaving out a letter") is a kind of constrained writing or word game consisting of writing paragraphs or longer works in which a particular letter or group of letters is avoided. Extended Ancient Greek texts avoiding the letter sigma are the earliest examples of lipograms.

Writing a lipogram may be a trivial task when avoiding uncommon letters like Z, J, Q, or X, but it is much more challenging to avoid common letters like E, T, or A in the English language, as the author must omit many ordinary words. Grammatically meaningful and smooth-flowing lipograms can be difficult to compose. Identifying lipograms can also be problematic, as there is always the possibility that a given piece of writing in any language may be unintentionally lipogrammatic. For example, Poe's poem The Raven contains no Z, but there is no evidence that this was intentional.

A pangrammatic lipogram is a text that uses every letter of the alphabet except one. For example, "The quick brown fox jumped over the lazy dog" omits the letter S, which the usual pangram includes by using the word jumps.

Lasus of Hermione, who lived during the second half of the sixth century BCE, is the most ancient author of a lipogram. This makes the lipogram, according to Quintus Curtius Rufus, "the most ancient systematic artifice of Western literature". Lasus did not like the sigma, and excluded it from one of his poems, entitled Ode to the Centaurs, of which nothing remains; as well as a Hymn to Demeter, of which the first verse remains:

The Greek poets from late antiquity Nestor of Laranda and Tryphiodorus wrote lipogrammatic adaptations of the Homeric poems: Nestor composed an Iliad, which was followed by Tryphiodorus' Odyssey. Both Nestor's Iliad and Tryphiodorus' Odyssey were composed of 24 books (like the original Iliad and Odyssey) each book omitting a subsequent letter of the Greek alphabet. Therefore, the first book omitted alpha, the second beta, the third gamma, and so forth.

Twelve centuries after Tryphiodorus wrote his lipogrammatic Odyssey, in 1711, the influential London essayist and journalist Joseph Addison commented on this work (although it had been lost), arguing that "it must have been amusing to see the most elegant word of the language rejected like "a diamond with a flaw in it" if it was tainted by the proscribed letter".

Petrus Riga, a canon of Sainte-Marie de Reims during the 11th century, translated the Bible, and due to its scriptural obscurities called it Aurora. Each canto of the translation was followed by a resume in Lipogrammatic verse; the first canto has no A, the second has no B, the third has no C, and so on. There are two hundred and fifty manuscripts of Petrus Riga's Bible still preserved.

There is a tradition of German and Italian lipograms excluding the letter R dating from the seventeenth century until modern times. While some authors excluded other letters, it was the exclusion of the R which ensured the practice of the lipogram continued into modern times. In German especially, the R, while not the most prevalent letter, has a very important grammatical role, as masculine pronouns, etc. in the nominative case include an R (e.g. er, der, dieser, jener, welcher). For the Italian authors, it seems to be a profound dislike of the letter R which prompted them to write lipograms excluding this letter (and often only this letter).