We have seen that Marx is committed to the view, which forms a cornerstone of environmental thought, that humans are dependent upon their natural environment. This view, I argued in the last chapter, is not contradicted by the idea that it is characteristic of humans to transform their environment. Nor, I argued in chapter 2, is a striving for economic or productive growth per se, in conflict with a recognition of the finitude of the natural resources upon which the species depends. It is clear, however, that of the different ways in which humans may transform nature, and expand their transformative powers, only some will be compatible with the avoidance or minimisation of ecological problems. It is therefore not sufficient to consider transformation of nature in the abstract; what is required is an examination of the particular account of the transformation of nature given by Marx, at the centre of which is his notion of the development of the productive forces. My aim in this chapter is therefore to consider how this notion should be understood and the role that it plays in Marx's theory, and to address the contention of many of Marx's green critics that his use of the notion leads inevitably to the exacerbation of ecological problems. More speculatively, I will suggest reasons why the notion may be a productive one for investigating ecological problems.