Composite materials are attractive as they can combine the superior properties and functionalities of each of their constituents. Much of current research focuses on developing multifunctional composites, which unite good mechanical (structural) attributes along with functional properties such as thermal, electrical, or magnetic characteristics. A particularly interesting example of such a composite consists of ferromagnetic microwires embedded in a polymer matrix, which is the main theme of the current book. These composites can exploit phenomena occurring in the wires such as the giant magnetoimpedance effect and can also offer emergent properties that arise from the mesoscale arrangement of the microwires (so-called metacomposites). Possible applications include remote monitoring of structural integrity, electromagnetic shielding, and cloaking at microwave wavelengths. The book should be therefore of general interest to researchers working on functional composite materials, especially for those working on electromagnetic composites and metacomposites. The fundamental theory and technical know-how provided in the book should also be useful for students and composite engineers.