Book excerpt: This book honours the contribution of Marjolijn Verspoor to the development and implementation of dynamic usage-based (DUB) approaches in second language (L2) research and pedagogy. With chapters written by renowned experts in the field, the book addresses the dynamics of language, language learning and language teaching from a usage-based perspective. The book contains both theory and empirical work: the initial theoretical chapters present cutting-edge thinking in relation to both the scope of DUB theory and its applications, providing conceptual perspectives from cognitive grammar and linguistics, thinking-for-speaking (TFS), and Complex Dynamic Systems Theory (CDST) approaches, united by their shared underpinnings of language as a dynamic system of conventionalized routines. The second half of the volume showcases state-of-the-art methodologies to study dynamic trajectories of language learning, empirical investigations into the above-mentioned theoretical concepts, and innovative classroom implementations of DUB language pedagogy.