Formal epistemology is the study of crucial concepts in general or mainstream epistemology including knowledge, belief (-change), certainty, rationality, reasoning, decision, justification, learning, agent interaction and information processing using a spread of different formal tools. These formal tools may be drawn from fields such as logic, probability theory, game theory, decision theory, formal learning theory, and distributed computing – such variety is typical in formal epistemology, a field in which interaction with topics outside of philosophy proper is the rule rather than the exception. Practitioners of formal epistemology include philosophers, computer scientists, social scientists, cognitive psychologists, theoretical economists, mathematicians, and theoretical linguists. The interdisciplinary nature of formal epistemology can make it difficult for those new to the field to have a sense of some of its basic agendas, actors, and issues. What follows is a breezy overview of formal epistemology as organized around notions of agency and interaction.