Volatile organic compounds (VOCs) are chemicals that have a high vapour pressure at room temperature. This high pressure results from a low boiling point, which causes large numbers of molecules to evaporate or sublimate from the liquid or solid form of the compound and enter the surrounding air, a trait known as 'volatility'. For example, formaldehyde, which evaporates from paint and releases from materials like quartz, has a boiling point of only -19 °C (-2 °F).

VOCs are numerous, varied, and ubiquitous. They include both human-made and naturally occurring chemical compounds. Most scents or odours are in effect VOCs. These compounds play an important role in communication between plants, and messages from plants to animals. Some VOCs are dangerous to human health or cause harm to the environment. Anthropogenic VOCs are regulated by law, especially indoors, where concentrations are the highest. Harmful VOCs are typically not acutely toxic, but have compounding long-term health effects. Because the concentrations are usually low, and the symptoms slow to develop, research into VOCs and their effects is difficult.