The article provides a comprehensive overview of formaldehyde, a versatile chemical compound with significant industrial and environmental applications. Formed from the dehydration of methanol, formaldehyde has been widely used in various industries since the 19th century. Its health effects, particularly as an indoor pollutant, have been extensively studied, leading to regulations and guidelines to limit exposure. The article discusses the physical and chemical properties of formaldehyde, its toxicology, and its applications in adhesives, coatings, and other materials. It also reviews the sources of formaldehyde, both outdoor and indoor, including natural and anthropogenic emissions. The chapter on sampling and analysis covers in-situ methods, derivatization techniques, and sensor technologies, highlighting the challenges and advancements in measuring formaldehyde levels. Finally, the article addresses emission testing using chambers and cells, emphasizing the importance of controlled environments in assessing formaldehyde emissions from building materials.The article provides a comprehensive overview of formaldehyde, a versatile chemical compound with significant industrial and environmental applications. Formed from the dehydration of methanol, formaldehyde has been widely used in various industries since the 19th century. Its health effects, particularly as an indoor pollutant, have been extensively studied, leading to regulations and guidelines to limit exposure. The article discusses the physical and chemical properties of formaldehyde, its toxicology, and its applications in adhesives, coatings, and other materials. It also reviews the sources of formaldehyde, both outdoor and indoor, including natural and anthropogenic emissions. The chapter on sampling and analysis covers in-situ methods, derivatization techniques, and sensor technologies, highlighting the challenges and advancements in measuring formaldehyde levels. Finally, the article addresses emission testing using chambers and cells, emphasizing the importance of controlled environments in assessing formaldehyde emissions from building materials.