Many scholars have concluded that teacher education research needs to take a complex view, resist simplification, and account more fully for teacher education's contexts and processes as well as its impact on teacher candidates' and school students' learning (Cochran-Smith & Zeichner, 2005; Grossman & McDonald, 2008; Opfer & Pedder, 2011). In this article, we describe a research platform for initial teacher education, developed by the Project RITE (Rethinking Initial Teacher Education) research team, which combines key ideas from complexity theory and critical realism (CT-CR) and applies these to teacher education. Our intention in referring to CT-CR as a research "platform" is to suggest that the integration of complexity theory and critical realism offers a potentially powerful framework for exploring how initial teacher education programs and pathways function as complex systems and why their outcomes are so uncertain and variable. In this article, we suggest that as a research platform, CT-CR has the capacity to open up new questions, point to new places to look for explanations, and offer new ways of understanding the initial conditions, system interactions, and underlying causal mechanisms involved in initial teacher education. In particular, we suggest that the CT-CR platform may support studies of the extent to which teacher candidates learn to engage in patterns of practice that support the learning of students who have been historically marginalized on the basis of race, culture, language, class and gender. The primary purpose of this article is conceptual in that it is intended to describe CT-CR as a research platform for initial teacher education. To achieve this purpose, the article includes multiple examples of the questions, research methods, and analyses researchers have developed, guided by complexity theory and/or critical realism. In addition, we use our own emerging program of research in Project RITE as a concrete in-progress example that elaborates the CT-CR framework and illustrates some of its applications to initial teacher education research.