The concept of human security is a highly contested one. Debate has centred largely on two disputes: one between advocates and critics of the concept, and the other, located within the human security family, between the proponents of broad and narrow definitions of the concept. This chapter explores these disagreements and the continuing problems in building a common definition of human security. The chapter goes on to develop general rules of thumb which can help determine which actors bear what responsibilities in the area of human security, and how these responsibilities are to be exercised. The chapter argues that clear criteria must be elaborated to guide the division and coordination of functions and responsibilities. National governments and civil society organisations (including the academy) that are sympathetically disposed to human security as well as the UN system have important roles to play in this complex and on-going task of elucidation.