Commercial and research interest in nanotechnology has exploded in recent years, with nearly US$9 billion in investment from public and private sources in 2005. While the list of potential applications for nanotechnologies continues to grow, there is increasing pressure from governments and researchers alike to understand the implications of this new class of materials. The emerging field of green nano applies green chemistry and engineering principles to the synthesis of nanomaterials. Here we outline several strategies for the development of green nano and review past policy and research activities in understanding nanotechnology's environmental implications. By means of the green chemistry metric of E-factor, an analysis is undertaken of the traditional syntheses of several specific nanomaterials, including carbon nanotubes, fullerenes, and metal nanoparticles. It was found that the E-factors of these production processes vary over several orders of magnitude, making it difficult to comment generally about the resource use efficiencies of nanomaterials production. For gold nanoparticles specifically, E-factors for six different production methods are found to range from 102 to 105, demonstrating that greener synthesis routes are possible and that environmental benefits can begin to be quantified. Expanding the analysis to include life-cycle stages upstream and downstream of production and to incorporate environmental health effects is encouraged, though significant data gaps exist.