This chapter summarizes information about volatile organic compounds (VOCs). This large and diverse group includes thousands of carbon-based substances with a wide range of boiling points and various chemical and physical properties. In addition to natural sources, human activities such as incomplete combustion (e.g., motor vehicle exhaust), fuel evaporation, fugitive emissions from industrial processes and applications (like solvent use), and biological processes like plant metabolism are important sources. Indoor air sources, including building materials, furniture, paint, smoking, and the use of cleaning products or cosmetics, largely contribute to human exposure. Therefore, a brief overview of the chemical and physical properties, usage patterns, main health risks, and toxicokinetics of various VOCs is provided, along with references to scientific literature. The primary goal is to provide detailed information on their presence in human matrices, such as blood, urine, and breast milk. Special emphasis is given to volatile organic compounds, aldehydes, glycol ethers, isothiazolinones, and methacrylates.