A spelling reform is a deliberate, often authoritatively sanctioned or mandated change to spelling rules. Proposals for such reform are fairly common, and over the years, many languages have undergone such reforms. Recent high-profile examples are the German orthography reform of 1996 and the on-off Portuguese spelling reform of 1990, which is still being ratified.

There are various goals which may drive such reforms: facilitating literacy and international communication, making etymology clearer, or for aesthetic or political reasons.

Opposition is often based upon concern that old literature will become inaccessible, the presumed suppression of regional accents, the need to learn the new spellings, making etymology less clear, or simple conservatism based on concern over unforeseen effects. Reforms which mainly eliminate needless difficulties ought to take account of such arguments. Reform efforts are further hampered by habit and, for many languages, a lack of a central authority to set new spelling standards.

Spelling reform may also be associated with wider discussion about the official script, as well as language planning and language reform.

Orthographic reform may be reverted. In Romanian, the letter â was eliminated in 1953 but reintroduced in 1993.

In languages written with a phonetic script (such as an alphabet, syllabary, abugida or, to a lesser extent, abjad), one might expect that there would be a close match of the script or spelling with the spoken sound. However, even if they match at one time and place for some speakers, over time they often do not match well for the majority: one sound may be represented by various combinations of letters and one letter or group of letters pronounced differently. In cases where spelling takes account of grammatical features, these too may become inconsistent.

People who use non-standard spelling often suffer from adverse opinions, as a person's mastery of standard spelling is often equated to their level of formal education or intelligence. Spelling is easier in languages with more or less consistent spelling systems, such as Finnish, Serbian, Italian and Spanish, owing either to the fact that pronunciation in these languages has changed relatively little since the establishment of their spelling systems, or the fact that non-phonemic etymological spellings have been replaced with phonemic unetymological spellings as pronunciation changed. Guessing the spelling of a word is more difficult after pronunciation changes significantly, thus yielding a non-phonetic etymological spelling system such as Irish or French. These spelling systems are still 'phonemic' (rather than 'phonetic') since pronunciation can be systematically derived from spelling, although the converse (i.e. spelling from pronunciation) may not be possible. English is an extreme example of a defective orthography in which spelling cannot be systematically derived from pronunciation, but it also has the more unusual problem that pronunciation cannot be systematically derived from spelling.

Spelling reforms have been proposed for various languages over the years; these have ranged from modest attempts to eliminate particular irregularities (such as SR1 or Initial Teaching Alphabet) through more far-reaching reforms (such as Cut Spelling) to attempts to introduce a full phonemic orthography, like the Shavian alphabet or its revised version, Quikscript, the latest DevaGreek alphabet, the Latinization of Turkish or hangul in Korea.