Most stars of the upper HRD live in multiple systems. When the separation is small, interactions may occur, affecting the stellar evolution and feedback. The presence of magnetic fields here opens the door to phenomena beyond the "usual" ones (mass transfer, wind collisions, tidal interactions,...) but it also put strong constraints on models of stellar evolution and magnetic field generation. This is why surveys of intermediate- and high-mass binaries with short periods have been undertaken. We will review results in this domain, including the properties of the (rare) detected cases such as Plaskett's star.