International audience During the last 50 years, the question of the cognitive nature of phonological units has followed the rhythm of the persistent debate between auditory and motor theories of speech communication. Though recent advances in cognitive neuroscience and cognitive psychology have largely renewed this debate, a consensus is still out of reach, and the true nature of speech units in the human brain remains elusive.A dimension of importance in this debate is a systemic one: speech units are not isolated, they are part of a phonological system, and they obey structural principles regarding well-investigated properties as distinctiveness, compositionality, contextual dependencies or systemic regularities. The phonological system itself is also part of a complex network of interaction with low-level biomechanical and sensory-motor systems, with higher-level brain structures regulating cognition, emotion and motivation, and finally with the social structures in which all these systems are embedded.Connecting assumptions or theories about the nature of speech units with a structuralist view about the relationship between phonetic properties and phonological systems has given rise to a number of major breakthroughs in speech science, for instance Lindblom’s bridges between the Variable Adaptive Theory (or its Hyper-Hypo variant) of speech communication (Lindblom, 1990) and the Dispersion Theory of vowel systems (Lindblom, 1986); or Stevens’ Quantal Theory (Stevens, 1972, 1989) addressing both the invariance issue and the search for the origins of distinctiveness and phonetic features; or the tandem between the Motor Theory of Speech Perception (Liberman & Mattingly, 1985) and Articulatory Phonology (Browman & Goldstein, 1992) in the Haskins Labs. This Special Issue is centered around a target paper by Moulin-Frier et al. that aims at relating the question of the auditory vs. motor vs. perceptuo-motor nature of speech units with simulations of vowel, plosive and syllable systems of human languages emerging from agent interactions, in a computational Bayesian framework. In this context, the papers in the special issue explore further the systemic perspective, studying how various dimensions of physical, cognitive, motivational and interactional systems can inform our understanding of the origins of speech forms.