This article focuses on the challenges of gathering, presenting, and using evidence that shapes deliberate and systematic religious engagement linked to international development and humanitarian programs. It sets the topic in a historical context, exploring the abrupt shift from a general neglect of religious dimensions by many institutions to the contemporary rising interest across wide-ranging institutions. It explores the “state of the art” today, asking what knowledge is available focused specifically on religion and development and in what disciplines, pertinent research (actual and emerging), and various relevant literature reviews that assess bodies of evidence.