Paul Constant Billot (12 March 1796 – 19 April 1863) was a French botanist born in Rambervillers.
He studied at the University of Strasbourg, subsequently leaving school due to illness. From 1830 he worked as a civil servant (conductor of ponts et chaussées), earning his bachelor's degree a few years later. From 1834 to 1861 he taught classes in physics and natural history in Haguenau.
With botanist Friedrich Wilhelm Schultz (1804–1876), he was co-author of Archives de la flore de France et d'Allemagne. Billot's Annotations a la flore de France et d'allemagne (1855) was issued with Flora galliae et germaniae exsiccata, a series which after his death in 1863 was continued by other scientists under the title of "Billotia".
Today his herbarium is kept at the Muséum d'histoire naturelle in Nantes.