The hexagonal ferrites, also known as hexaferrites, have become massively important materials commercially and technologically, accounting for the bulk of the total magnetic materials manufactured globally, and they have a multitude of uses and applications. As well as their use as permanent magnets, common applications are as magnetic recording and data storage materials, and as components in electrical devices, particularly those operating at microwave/GHz frequencies for mobile and wireless communications, electromagnetic wave absorbers for electromagnetic compatibility (EMC), radar absorbing materials (RAM) and stealth technologies. One of the most exciting recent developments has been the discovery of single phase magnetoelectric/multiferroic hexaferrites, firstly Ba2Mg2Fe12O22 Y-type ferrite at cryogenic temperatures, and more recently Sr3Co2Fe24O41 Z-type ferrite at room temperature. Several Y-type, substituted M-type, and U-type (Sr4Co2Fe36O60) ferrites have now been characterised as room temperature multiferroics, and are discussed in this chapter.