Smilei is an open-source, user-friendly electromagnetic particle-in-cell code for the kinetic simulation of plasmas. Co-developed by physicists and computer scientists, it is designed for high-performance on the most recent supercomputing architectures. Smilei is applied to a wide range of applications, from laser-plasma interaction, to accelerator physics, space physics and astrophysics. It is also used at the bachelor and master levels as a teaching platform for plasma physics.