Recent advances in our understanding of complex composite media, especially chiral media for microwave applications, suggest the feasibility of creating novel materials with unusual properties and the possibility of constructing new microwave devices using such materials. The emphasis of the book is on bi-anisotropic materials, whose most interesting feature is the magnetoelectric interaction of the fields. The materials are expected to supply useful applications in radar technology, aerospace, microwave engineering, manufacturing technology, etc., such as absorbers for low-reflectivity shields, reciprocal phase shifters, polarization transformers. The first experiments with artificial bi-anisotropic media have been successfully carried out.