Doubly articulated consonants are consonants with two simultaneous primary places of articulation of the same manner (both plosive, or both nasal, etc.). They are a subset of co-articulated consonants. They are to be distinguished from co-articulated consonants with secondary articulation, that is, a second articulation not of the same manner. An example of a doubly articulated consonant is the voiceless labial–velar plosive [k͡p], which is a [k] and a [p] pronounced simultaneously. On the other hand, the voiceless labialized velar plosive [kʷ] has only a single stop articulation, velar ([k]), with a simultaneous approximant-like rounding of the lips. In some dialects of Arabic, the voiceless velar fricative [x] has a simultaneous uvular trill, but this is not considered double articulation either.
There are four independently controllable articulations that may double up in the same manner of articulation: labial, coronal, dorsal, and radical. (The glottis controls phonation, and works simultaneously with many consonants. It is not normally considered an articulator, and an ejective [kʼ], with simultaneous closure of the velum and glottis, is not considered a doubly articulated consonant.)
Approximants such as [w] and [ɥ] may be either doubly or secondarily articulated. For example, in English, /w/ is a labialized velar that could be transcribed as [ɰʷ], but the Japanese /w/ is closer to a true labial–velar [ɰ͡β̞]. However, it is normal practice to use the symbols ⟨w⟩ and ⟨ɥ⟩ for the labialized approximants, and some linguists restrict the symbols to that usage. (See the article on approximants.)
No claims have ever been made for doubly articulated flaps or trills, such as a simultaneous alveolar–uvular trill, *[ʀ͡r], and these are not expected to be found. Several claims have been made for doubly articulated fricatives or affricates, most notoriously a Swedish phoneme which has its own IPA symbol, [ɧ]. However, laboratory measurements have never succeeded in demonstrating simultaneous frication at two points of articulation, and such sounds turn out to be either secondary articulation, or a sequence of two non-simultaneous fricatives. (Despite its name, the "voiceless labial-velar fricative" [ʍ] is actually a voiceless approximant; the name is a historical remnant from before the distinction was made.) Such sounds can be made, with effort, but it is very difficult for a listener to discern them, and therefore they are not expected to be found as distinctive sounds in any language.
Clicks are doubly articulated by definition: they involve a coronal (more rarely labial) forward articulation, or release, plus a dorsal closure that pulls double duty, both as the second place of articulation, and as the controlling mechanism of the velaric ingressive airstream. (Some of these clicks are uvular, rather than velar, but the term "velaric ingressive airstream" is used as the general term. See the article on clicks.)
This leaves stops, and both oral and nasal doubly articulated stops are found. However, there is a great asymmetry in the places of their articulation. Of the six possible combinations of labial, coronal, dorsal, and radical, one is common, and the others vanishingly rare.