Dynamic Assessment (DA) is an alternative to traditional approaches to language testing that merges teaching and assessment based on the framework of Vygotsky’s sociocultural theory, which views learning as socially mediated, focusing on what learners can develop in their Zone of Proximal Development. DA is conducted using interactionist or interventionist approaches, with the benefits that each provides to a particular teaching situation. DA has been shown through empirical studies to be an effective means of helping learners acquire the grammar of their second language, build their lexicon, or learn the target language at all levels of competence. If evaluation is turned from a black box into a part of the learning loop, DA offers teachers the possibility to use it not only as a diagnostic device, but also in order to foster learning processes. This paper discusses some of the theoretical underpinnings of DA and reviews what is known about using DA for teaching a second language (SL) and describes the implications of this for future teaching and assessment practice.