This article extends our understanding of the firm–nongovernmental organization relationship by emphasizing the role of language in shaping organizational behavior. It focuses on discursive and rhetorical activity through which firms and NGOs jointly – and not always consciously – define boundaries for socially acceptable corporate behavior. It explores the discursive legitimation struggles of a leading Finnish forest industry company StoraEnso and Greenpeace during 1985–2001 and examines how these struggles participated in the definition and institutionalization of corporate social responsibility. I find (...) a mixture of rational and moral struggles as a key feature of this legitimation work and show how different manifestations of these struggles act as a central mechanism that redefines what the boundaries of corporate responsibility are in a specific setting at a given point of time. The study illustrates how the actors’ ability to sense the public’s views contribute to rhetorical difficulties of the industry and unintended societal consequences for the activists, and how the rational and moral struggles build up in time to trigger changes in the actors’ sensemaking and actions. (shrink)