Language reform is a kind of language planning by widespread change to a language. The typical methods of language reform are simplification and linguistic purism. Simplification regularises vocabulary, grammar, or spelling. Purism aligns the language with a form which is deemed 'purer'.

Language reforms are intentional changes to language; this article does not cover natural language change, such as the Great Vowel Shift.

By far the most common language reform is simplification. The most common simplification is spelling reform, but inflection, syntax, vocabulary and word formation can also be targets for simplification. For example, in English, there are many prefixes which mean "the opposite of", e.g. un-, in-, a(n)-, dis-, and de-. A language reform might propose to replace the redundant prefixes with one, such as un-.

Linguistic purism or linguistic protectionism is the prescriptive practice of recognising one form of a language as purer or of intrinsically higher quality than others. The perceived or actual decline may take the form of change of vocabulary, syncretism of grammatical elements, or loanwords, and in this case, the form of a language reform.

Examples of language reforms are: