There has been much recent attention, and in some cases concern, about airborne exposure to nanoparticles (generally meaning aerodynamic diameters less than 100 µm) associated with engineered nanomaterials. While there are valid questions about these potentials exposures, it is important to understand that so-called incidental nanoparticles are common in outdoor air and are also released from many normal residential activities, e.g. cooking. This presentation explains how airborne nanoparticles are measured, summarize measurements of incidental nanoparticles in a residential environment, and discusses some examples of how engineered nanomaterials in residential environments could be a source of exposure.