The concept of autonomy plays important roles in clinical practice, medical research, and public health. While there is agreement that autonomy is an important kind of individual freedom, there are different ways of conceptualizing what autonomy is and understanding what conditions an action or agent should meet to count as autonomous. Different conceptions of autonomy will have differing implications for health care practices and policies. This chapter overviews several of the main ways autonomy has been conceived, examining libertarian conceptions, the “informed consent” approach, reflective endorsement accounts, substantive theories, autonomy competency accounts, and relational theories. For each of these approaches, the chapter will examine the reasons for thinking it helps capture the concept of autonomy, the resulting understanding of what conditions an action or agent should meet to be autonomous, and its implications in different contexts of health care, medical research, and for public health policies or programs.