This chapter focuses on waste regulation and how the notion of ‘waste’, which can give rise to serious environmental and health problems, is a legally constructed one. Unlike other pollution control regimes, waste regulation is focused on an identified pollution source, which is defined and characterized in legal terms. The chapter shows how difficult it can be to make the legal distinction between waste and non-waste. In regulating waste, there is a fundamental tension between minimizing the polluting impacts of waste (making waste a firm focus for regulation), and encouraging secondary markets that promote discarded material as a resource rather than a potential pollution problem (where ‘waste’ can be a poor characterization of material). Legal disputes over the definition of waste and how waste should be regulated are grappling with this policy tension in an increasingly circular economy for natural resources.