The capitalist system cannot exist without unlimited “development,” “growth,” “expansion,”and it is leading,in the next few decades,to an ecological catastrophe without precedent in human history. A radical alternative must therefore be an anticapitalist one.Ecosocialism is one such antisystemic alternative.It is a current of ecological thought and action that appropriates the fundamental gains proposed in Marxism, while shaking off any productivist dross. Ecosocialists see both the logic of markets and the logic of bureaucratic authoritarianism,as it existed in the former USSR,as incompatible with the need to safeguard the environment in general and the climate in particular. Ecosocialism is an attempt to provide a radical civilizational alternative,based on the basic arguments of the ecological movement,and of the Marxist critique of political economy.