Postalveolar (post-alveolar) consonants are consonants articulated with the tongue near or touching the back of the alveolar ridge. Articulation is farther back in the mouth than the alveolar consonants, which are at the ridge itself, but not as far back as the hard palate, the place of articulation for palatal consonants. Examples of postalveolar consonants are the English palato-alveolar consonants [ʃ] [tʃ] [ʒ] [dʒ], as in the words "ship", "'chill", "vision", and "jump", respectively.

There are many types of postalveolar sounds—especially among the sibilants. The three primary types are palato-alveolar (such as [ʃ ʒ], weakly palatalized; also alveopalatal), alveolo-palatal (such as [ɕ ʑ], strongly palatalized), and retroflex (such as [ʂ ʐ], unpalatalized). The palato-alveolar and alveolo-palatal subtypes are commonly counted as "palatals" in phonology since they rarely contrast with true palatal consonants.

For most sounds involving the tongue, the place of articulation can be sufficiently identified just by specifying the point of contact on the upper part of the mouth (for example, velar consonants involve contact on the soft palate and dental consonants involve the teeth), along with any secondary articulation such as palatalization (raising of the tongue body) or labialization (lip rounding).

However, among sibilants, particularly postalveolar sibilants, there are slight differences in the shape of the tongue and the point of contact on the tongue itself, which correspond to large differences in the resulting sound. For example, the alveolar fricative [s] and the three postalveolar fricatives [ɕ ʃ ʂ] differ noticeably both in pitch and sharpness; the order [s ɕ ʃ ʂ] corresponds to progressively lower-pitched and duller (less "hissy" or piercing) sounds. ([s] is the highest-pitched and most piercing, which is the reason that hissing sounds like "Sssst!" or "Psssst!" are typically used to attract someone's attention). As a result, it is necessary to specify many additional subtypes.

The main distinction is the shape of the tongue, which corresponds to differing degrees of palatalization (raising of the body of the tongue). From least to most palatalized, they are retroflex (such as [ʂ ʐ], unpalatalized); palato-alveolar (such as [ʃ ʒ], weakly palatalized); and alveolo-palatal (such as [ɕ ʑ], strongly palatalized). The increasing palatalization corresponds to progressively higher-pitched and sharper-sounding consonants.

Less technically, the retroflex consonant [ʂ] sounds somewhat like a mixture between the regular English [ʃ] of "ship" and the "h" at the beginning of "heard", especially when it is pronounced forcefully and with a strong American "r". The alveolo-palatal consonant [ɕ] sounds like a strongly palatalized version of [ʃ], somewhat like "nourish you".

The following table shows the three types of postalveolar sibilant fricatives defined in the IPA:

A second variable is whether the contact occurs with the very tip of the tongue (an apical articulation [ʃ̺]), with the surface just above the tip, the blade of the tongue (a laminal articulation [ʃ̻]), or with the underside of the tip (a subapical articulation). Apical and subapical articulations are always "tongue-up", with the tip of the tongue above the teeth, and laminal articulations are often "tongue-down", with the tip of the tongue behind the lower teeth.