Given its widespread use in construction, textiles, and myriad wood and consumer products, exposure to formaldehyde has become difficult to avoid. On a daily basis, people in the general population are exposed to formaldehyde indoors, outdoors, occupationally, and environmentally but most of them are largely unaware of these sources of exposure and related adverse health effects. As described here, regulation of formaldehyde in exposure settings varies by country, as there is no worldwide consensus on what constitutes a “safe” level of formaldehyde exposure. In this chapter, sources and concentrations of indoor and outdoor air exposure, major routes of exposure, and the metabolic fate of formaldehyde in humans are detailed.