An orthography is a set of conventions for writing a language, including norms of spelling, punctuation, word boundaries, capitalization, hyphenation, and emphasis.

Most national and international languages have an established writing system that has undergone substantial standardization, thus exhibiting less dialect variation than the spoken language. These processes can fossilize pronunciation patterns that are no longer routinely observed in speech (e.g. would and should); they can also reflect deliberate efforts to introduce variability for the sake of national identity, as seen in Noah Webster's efforts to introduce easily noticeable differences between American and British spelling (e.g. honor and honour).

Orthographic norms develop through social and political influence at various levels, such as encounters with print in education, the workplace, and the state. Some nations have established language academies in an attempt to regulate aspects of the national language, including its orthography—such as the Académie Française in France and the Royal Spanish Academy in Spain. No such authority exists for most languages, including English. Some non-state organizations, such as newspapers of record and academic journals, choose greater orthographic homogeneity by enforcing a particular style guide or spelling standard such as Oxford spelling.

The English word orthography is first attested in the 15th century, ultimately from Ancient Greek: ὀρθός (orthós 'correct') and γράφειν (gráphein 'to write').

Orthography in phonetic writing systems is often concerned with matters of spelling, i.e. the correspondence between written graphemes and the phonemes found in speech. Other elements that may be considered part of orthography include hyphenation, capitalization, word boundaries, emphasis, and punctuation. Thus, orthography describes or defines the symbols used in writing, and the conventions that regulate their use.

Most natural languages developed as oral languages and writing systems have usually been crafted or adapted as ways of representing the spoken language. The rules for doing this tend to become standardized for a given language, leading to the development of an orthography that is generally considered "correct". In linguistics, orthography often refers to any method of writing a language without judgement as to right and wrong, with a scientific understanding that orthographic standardization exists on a spectrum of strength of convention. The original sense of the word, though, implies a dichotomy of correct and incorrect, and the word is still most often used to refer specifically to a standardized prescriptive manner of writing. A distinction is made between emic and etic viewpoints, with the emic approach taking account of perceptions of correctness among language users, and the etic approach being purely descriptive, considering only the empirical qualities of any system as used.

Orthographic units, such as letters of an alphabet, are conceptualized as graphemes. These are a type of abstraction, analogous to the phonemes of spoken languages; different physical forms of written symbols are considered to represent the same grapheme if the differences between them are not significant for meaning. Thus, a grapheme can be regarded as an abstraction of a collection of glyphs that are all functionally equivalent. For example, in written English (or other languages using the Latin alphabet), there are two different physical representations (glyphs) of the lowercase Latin letter a: ⟨a⟩ and ⟨ɑ⟩. Since the substitution of either of them for the other cannot change the meaning of a word, they are considered to be allographs of the same grapheme, which can be written |a|. The italic and boldface forms are also allographic.

Graphemes or sequences of them are sometimes placed between angle brackets, as in |b| or |back|. This distinguishes them from phonemic transcription, which is placed between slashes (/b/, /bæk/), and from phonetic transcription, which is placed between square brackets ([b], [bæk]).