Environmentalism, in all its forms, was born in environmental movements. There are many theories about what makes up a social movement, and some of these are outlined in this chapter. At the outset, what needs to be understood is that social movements occupy a political terrain that is often quite separate from more established institutionalized political forms such as pressure groups, parties, and the administrative and parliamentary systems of the state. This terrain is called ‘civil society’ or the ‘third sector’ – the two other sectors being the state and the market. It includes groups and organizations dedicated to expressing the interests of the citizenry. It was within these more informal realms of society that environmental movements emerged. It is safe to say that without the environmental movements there would be little or no ‘greening’ of government or corporations.