| Mathieu Orfila | |
| Birth Date: | 24 April 1787 |
| Birth Place: | Mahón, Menorca, Kingdom of Spain |
| Death Date: | 12 March 1853 (aged 65) |
| Death Place: | Paris, Île-de-France, French Empire |
| Citizenship: | Spanish |
| Nationality: | Spanish |
| Field: | Toxicology and chemistry |
| Alma Mater: | University of Valencia University of Barcelona |
| Known For: | Founded toxicology |
Mathieu Joseph Bonaventure Orfila (Catalan: Mateu Josep Bonaventura Orfila i Rotger) (24 April 1787 - 12 March 1853) was a Spanish toxicologist and chemist, the founder of the science of toxicology.
If there is reason to believe that a murder or attempted murder may have been committed using poison, a forensic toxicologist pharmaceutical is often engaged to examine pieces of evidence such as corpses and food items for poison content. In Orfila's time the primary type of poison in use was arsenic, but there were not any reliable ways of testing for its presence. Orfila created new techniques, refined existing techniques and described them in his first treatise, Traité des poisons (1813), greatly enhancing their accuracy.
In 1840, Marie Lafarge was tried for the murder of her husband. Although she had had access to arsenic, and arsenic had been found in the victim's food, none could be found in the corpse. Orfila was asked by the court to investigate. He discovered that the test used, the Marsh test, had been performed incorrectly, and that there was in fact arsenic in the body; LaFarge was subsequently found guilty.