Since its inception as a field, the interdisciplinary nature of the Learning Sciences has led researchers to leverage, develop, refine and debate a wide variety of theories to better understand how to explain and support learning across diverse contexts. In this chapter, we outline the two most common: cognitive theories, which focus on the mental processes of the individual learner, and sociocultural theories, which focus on the participation of learners in social, cultural, and historical practices within a particular context. We briefly summarize the unique contributions of each theoretical perspective and how they have shaped our perception as a field. In particular, we note how each has explored knowledge, learning, transfer, and motivation. We then describe what we view as promising synergies that have arisen within the Learning Sciences, which build on and extend both these theoretical perspectives.