Language program evaluation is a pragmatic mode of inquiry that illuminates the complex nature of language-related interventions of various kinds, the factors that foster or constrain them, and the consequences that ensue. Program evaluation enables a variety of evidence-based decisions and actions, from designing programs and implementing practices to judging effectiveness and improving outcomes. Though often narrowly construed as an external accountability requirement only, evaluation may provide a heuristic for generating new knowledge; raising awareness; and transforming the educational, social, and economic circumstances of individuals and communities. In this article, I review the origins and interdisciplinary nature of program evaluation, and I trace its development within applied linguistics and language education in particular. I then consider the current contributions of language program evaluation, and I point to likely future trends. In particular, I highlight how changing global circumstances, technological affordances, and contexts and purposes for language learning and language use are both impacting the nature of evaluation and presenting challenges for which evaluation is uniquely suited to respond. I also emphasize the potential--versus as yet realized--contribution of program evaluation as a way of ameliorating gaps in current language research and practice, and I point to implications for training, dissemination, and integration of this mode of inquiry as an important part of the future intellectual core of applied linguistics.