This Technical Report has been prepared in response to ? increasing concern over the potential health risks associated with occupational exposure to nanometrediameter and nanometre-structured aerosol particles (collectively referred to as nanoaerosols, including the subset of particles produced as a by-product of industrial processes and generally referred to as ultrafine aerosols), ? the lack of current guidelines and standards applicable to minimizing the health risks, and ? the need to establish valid sampling methodologies as part of the process of formulating appropriate exposure and exposure monitoring standards.