The concept ‘ecosocialism’ is variously interpreted, with some analysts seeing it as a ‘red-green alliance’ that combines the Marxist critique of capitalism with environmental theory. Other theorists, such as Paul Burkett and John Bellamy Foster, argue that classical Marxism is inherently ecological and dispute that there is any need to introduce environmental theory into this body of thought. They point to Marx’s writings on the ‘metabolic rift’ to support their claims, and they also engage in ‘anti-critiques’ that respond to specific criticisms of Marxism’s ‘anti-ecological’ features. This chapter introduces the reader to some ecological critiques of classical Marxism – for instance, that it is ‘productivist,’ that it promotes ‘Prometheanism,’ and that it fails to account for the intrinsic value of nature – and responses by ‘second-stage ecosocialist’ theorists to these critiques. In addition to providing an overview of some of the internal debates that theorists who identify as ecosocialist engage in, this chapter also summarises some of the critiques that ecosocialists make of ‘ecomodernism’, which is a relatively recent current in environmental theory.