Marie Ennemond Camille Jordan (January 5 1838 – January 22 1922) was a French mathematician, known both for his foundational work in group theory and for his influential Cours d'analyse. He was born in Lyons and educated at the École polytechnique. He was an engineer by profession; later in life he taught at the École polytechnique and the Collège de France; where he had a reputation for eccentric choices of notation.

He is remembered now by name in a number of foundational results:

• the Jordan curve theorem, a topological result required in complex analysis;
• the Jordan normal form in linear algebra;
• in mathematical analysis, Jordan content is an area measure that predates measure theory;
• in group theory the Jordan-Hölder theorem on composition series is a basic result.

Jordan's work did much to bring Galois theory into the mainstream. He also investigated the Mathieu groups, the first examples of sporadic groups. His Traité des substitutions, on permutation groups, was published in 1870.

The asteroid 25593 Camillejordan is named in his honour.