变调（英语：Tone sandhi）又称为连续变调、连接变调，即是将声调变化之方法使用于字词音节并合上的处理。变调在梵文里意思为「合并在一起」。在所有的声调性语言里改变声调的进程是一种主动形态的作为，不过从某些方面看来也是一种语言上比较普遍性的声调并合运作形态。

变调亦存在于许多汉语族语言，如现代标准汉语、粤语、客家语、闽南语、莆仙语、闽东语、吴语与晋语中皆有此现象。现代标准汉语的变调规则比较简单，而莆仙语、闽东语的变调规则最为复杂。

Tone sandhi is a phonological change occurring in tonal languages, in which the tones assigned to individual words or morphemes change based on the pronunciation of adjacent words or morphemes. It usually simplifies a bidirectional tone into a one-direction tone. It is a type of sandhi, or fusional change, from the Sanskrit word for "joining".