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D ow nloaded from Nanotechnology is an emerging science involving manipulation of matter at the nanometer scale. Due to concerns over nanomaterial risks, there has been a dramatic increase in focused safety research. The present review provides a summary of these published findings, identifying areas of agreement and discordance with regard to: 1) the potential for nanomaterial exposure, 2) the relative hazard nanomaterials pose to humans and the environment, and 3) the present deficits in our understanding of risk. Special attention is paid to study design and methodologies, offering valuable insight into the complexities encountered with nanomaterial safety assessment. Recent data highlights the impact of surface characteristics on nanomaterial biocompatibility, and points to the inadequacy of the current size-dependent mechanistic paradigms, with nano-scale materials lacking unique or characteristic toxicity profiles. The available data supports the ability of the lung, gastrointestinal tract, and skin to act as a significant barrier to the systemic exposur