In linguistics, a distinctive feature is the most basic unit of phonological structure that distinguishes one sound from another within a language. For example, the feature [voice] distinguishes the two bilabial plosives: [p] and [b]. There are many different ways of defining and arranging features into feature systems: some deal with only one language while others are developed to apply to all languages.

Distinctive features are grouped into categories according to the natural classes of segments they describe: major class features, laryngeal features, manner features, and place features. These feature categories in turn are further specified on the basis of the phonetic properties of the segments in question. For phonemes to be in a particular natural class, they have to share the same distinctive features such as articulation and/or sound similar to each other. We can find distinctive features between two words by finding the minimal pair between them. The minimal pair are when two words sound the same, but they are different in definition because the pair has different phonemes from each other.

Since the inception of the phonological analysis of distinctive features in the 1950s, features traditionally have been specified by binary values to signify whether a segment is described by the feature; a positive value, [+], denotes the presence of a feature, while a negative value, [−], indicates its absence. In addition, a phoneme may be unmarked with respect to a feature. It is also possible for certain phonemes to have different features across languages. For example, [l] could be classified as a continuant or not in a given language depending on how it patterns with other consonants. After the first distinctive feature theory was created by Jakobson in 1941, it was assumed that the distinctive features are binary and this theory about distinctive features being binary was formally adopted in “Sound Pattern of English” by Chomsky and Halle in 1968. Jakobson saw the binary approach as the best way to make the phoneme inventory shorter and the phonological oppositions are naturally binary.

In recent developments to the theory of distinctive features, phonologists have proposed the existence of single-valued features. These features, called univalent or privative features, can only describe the classes of segments that are said to possess those features, and not the classes that are without them.