This chapter delves into the philosophical and sociological foundations of the principle of responsibility and explores how this concept has been applied to understand businesses’ agency and responsibility. The chapter further examines responsibility as a principle for motivating and justifying business action towards the circular economy, proposing the concept of circular business responsibility. To illustrate how the principle of responsibility operates within the circular economy, the chapter examines the role of Extended Producer Responsibility in global supply chains, showcasing successful voluntary initiatives that exemplify proactive producer responsibility.