Professor Henderson teaches and writes primarily in epistemology and the philosophy of the social sciences. Many of his interests in epistemology largely revolve around what it is to be justified in holding a belief. He has written on epistemological internalism and externalism, on various versions of reliabilism, on foundationalism and coherentism, on virtue epistemology, and on a priori justification. He is also interested in testimonial based knowledge, and in contextual accounts of knowledge. He is presently engaged with issues that include the epistemology of disagreement, social epistemology, and epistemic norms as social norms. These issues make for connections with his interests in the social sciences. His work in the philosophy of the social sciences has focused on the relations between interpretation and explanation, the place for attributions of rationality and irrationality, and the character of explanations in terms of norms.