Picard's little theorem states that every nonconstant entire function takes every value in the complex plane, with perhaps one exception.

In connection with his work on function theory, he was one of the first mathematicians to use the emerging ideas of algebraic topology.

In addition to his theoretical work, Picard made contributions to applied mathematics, including the theories of telegraphy and elasticity.

Louis Couturat studied integral calculus with Picard in 1891-1892, taking detailed notes of the lectures.

[4] Like his contemporary, Henri Poincaré, Picard was much concerned with the training of mathematics, physics, and engineering students.