Phlogiston was a scientific theory proposed in the 17th century to explain combustion and oxidation. According to this theory, all combustible materials contained a substance called phlogiston, which was released during burning. The more phlogiston a material had, the more flammable it was thought to be. The concept of phlogiston was eventually disproven by the work of Antoine Lavoisier, who demonstrated that combustion involves the combination of a substance with oxygen. This led to the modern understanding of chemical reactions and the development of the field of chemistry, rendering the phlogiston theory obsolete.