A multi-ferroïc material possesses simultaneously two or more ferroïc orders: ferroelectric, ferromagnetic and ferroelastic. Particularly fascinating is the coupling between these orders. For example magneto-electric coupling allows electrical control of the magnetization or, inversely, magnetic control of the polarization. The coupling coefficient α is defined by M=αP. Multi-ferroicity provides additional handles to control oxide properties. To these can be added collective orbital, spin and charge phenomena.