This article explores the work of French thinker Gilles Deleuze and argues for the application of his central ideas to the study of health and human development. Deleuze's work furnishes a host of ontological and epistemological resources for such analysis, ushering in new methods and establishing new objects of inquiry. Of principal interest are the inventive conceptualizations of affect, multiplicity and relationality that Deleuze proposes, and the novel reading of subjectivity that these concepts support. This article introduces a developmental ethology in exploring Deleuze's contributions to the study of human development and its varied courses and processes. Taken from a Deleuzean perspective, human development will be characterized as a discontinuous process of affective and relational encounters. It will be argued further that human development is advanced in the provision of new affective sensitivities and new relational capacities. This course is broadly consistent with existing approaches to human development--particularly those associated with Amartya Sen's capabilities model--with the considerable advantage of offering a more viable working theory of the ways in which developmental capacities are acquired, cultivated and maintained. A provisional research agenda consistent with this developmental ethology is offered by way of conclusion.