The Athabaskan languages have a particularly rich series of stop contrasts, plain stops and affricates, each exhibiting a three-way laryngeal contrast, unaspirated, aspirated and ejective. Several aspects of this inventory are interesting to phonetic and phonological studies, among them the length and ‘heaviness’ of the releases on the aspirated plain stops, the temporal properties of the ejectives, and the richness of the stop contrast set, approximately 21 distinct segments. This paper is an investigation of the phonetic realization of the stops in five Athabaskan languages: Dene Sųłiné (CL), Dene Sųłiné (FC), Dogrib, North Slavey, and Tsilhqut’in, compared with data from Navajo from McDonough [(2003). The Navajo sound system. Kluwer: Dordrecht]. Based on the phonetic patterns in the data, we argue that, among the consonants, the primary organizing feature of the contrasts is a temporal distinction, which we model as simplex–complex contrast, based on Laver [(1994). Principles of phonetics. Cambridge: Cambridge University Press], in which the temporal properties of medial phase of the segment's articulation play a significant role in the contrast. This classification represents a major divide in the inventory between the unaspirated plain stops (orthographically ( b) , d, g, ( q)) and the rest of the stops in the inventory. These data suggest first that aspirated plain stops (orthographically t, k) are mislabeled. Instead, in keeping with much of the early literature on the Athabaskan languages, the t and k phonemes are the affricates /tx, kx/. Second, related to this, long release periods are a characteristic feature of all but the unaspirated stops in the inventory. As such they represent a feature of a larger grouping in the Athabaskan inventory, realized in a temporal domain and persistent in the family, in a pattern likely inherited from the parent language. We model this temporal distinction as a simplex–complex distinction, which separates out the ‘unaspirated’ plain stops, as simplex segments with short offsets, from the rest of the stops, including the plain ‘aspirated’ stops and ejectives, which have complex medial phases with long release periods. Furthermore, the proposal suggests that the languages have exploited the sets of simplex stops and fricatives to build their rich inventories of complex segments, as several linguists have observed. The analysis serves as a basis for understanding sound change and alternation patterns in the family.