Intonation is the variation of tone used when speaking. Intonation and Vocal stress are the two elements of (linguistic) prosody.

Many languages use pitch syntactically, for instance to convey surprise and irony or to change a sentence from a statement to a question. Such languages are called intonation languages. English is a well-known example. Some languages use intonation to convey meaning. Languages in which the syllables are contrasted by pitch are known as tonal languages. Thai is an example. An intermediate position is occupied by languages with a melodic accent, for instance Swedish.

Rising intonation means the pitch of the voice goes up; falling intonation means that the pitch goes down. For example, northeastern American English has a rising intonation for questions, and a falling intonation for statements.

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In music, the word intonation is a synonym for tuning and systems of musical tuning. If musicians have "bad intonation", it means they play or sing out of tune.

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For a guitar intonation refers to the length of the strings relative to the position of the frets. Bad intonation refers to any error between them. Intonation can typically be adjusted through changing the bridge position (in effect changing the string length) and also by changing the neck angle (by adjusting the truss rod) or by changing the weight of the strings.

A common simple test for some intonation faults is to check that the harmonic at fret twelve is the exact same pitch as the note from the string when fretted at the same place. Normally this will be corrected by adjusting the bridge position.

A badly made or damaged guitar may have intonation so bad that it cannot be corrected without performing extensive work on the guitar (for example removing the neck and re-fixing in a different position or replacing the neck entirely).