Kelvin-Helmholtz Instability (KHI) is a fundamental plasma process driven by velocity shears, being ubiquitous in both fluids and plasmas. It has been observed in the magnetospheres of planets with (e.g. Earth, Mercury, Jupiter, Saturn) and without a magnetic field (e.g. Mars, Venus), as well as in the solar corona and solar wind at the boundary of coronal mass ejections. Contrary to neutral fluids, which are always unstable to KHI, in a magnetized environment, the magnetic field plays a crucial role acting as a stabilizer. As a driver of large-scale vortices along the boundary, KHI contributes to mass and momentum transport, enabling plasma mixing that would otherwise be limited in a highly magnetized environment. Moreover, as the instability grows, vortices become increasingly steepened and rolled-up. The nonlinear interaction of modes produces an energy cascade from the large-scale vortices to kinetic scales, where dissipation mechanisms such as wave-particle interactions and reconnection heat the plasma. The nonlinear evolution of KHI-generated vortices can trigger secondary processes or waves, such as Rayleigh-Taylor instability, lower hybrid waves, and generate thin current sheets where magnetic reconnection can occur, as well as develop a turbulent environment.