The central claims defended in this article are the following: (a) The social and ethical challenges of nanotechnology can be fully identified only if both the characteristic features of nanotechnologies and the social contexts into which they are emerging are considered. (b) When this is done, a host of significant social context issues, or issues that arise as a result of problematic features of the social contexts into which nanotechnology is emerging, become salient. (c) These issues can only be addressed by remedying the problematic features of the social contexts, which cannot be accomplished by technology design or risk management alone. (d) The U.S. National Nanotechnology Initiative's conceptualization and operationalization of responsible development does not adequately recognize the significance of social context issues to responsible development. (e) Therefore, the National Nanotechnology Initiative is not yet comprehensive and needs to be expanded with respect to identifying and addressing social context issues. (Contains 17 notes.)