Abstract: This introductory article for the Special Issue on Vocal Accommodation in Speech Communication provides an overview of prevailing theories of vocal accommodation and summarizes the ten papers in the collection. Communication Accommodation Theory focusses on social factors evoking accent convergence or divergence, while the Interactive Alignment Model proposes cognitive integration of perception and production as an automatic priming mechanism driving convergence language production. Recent research including most of the papers in this Special Issue indicates that a hybrid or interactive synergy model provides a more comprehensive account of observed patterns of phonetic convergence than purely automatic mechanisms. Some of the fundamental questions that this special collection aimed to cover concerned (1) the nature of vocal accommodation in terms of underlying mechanisms and social functions in human–human and human–computer interaction; (2) the effect of task-specific and talker-specific characteristics (gender, age, personality, linguistic and cultural background, role in interaction) on degree and direction of convergence towards human and computer interlocutors; (3) integration of articulatory, perceptual, neurocognitive, and/or multimodal data to the analysis of acoustic accommodation in interactive and non-interactive speech tasks; and (4) the contribution of short/long-term accommodation in human–human and human–computer interactions to the diffusion of linguistic innovation and ultimately language variation and change.