Metamaterials-engineered materials with rationally designed geometry, composition, and arrangement of nanostructured building blocks-are predicted to play an increasingly important role in high technologies of the twenty-žrst century. Unfortunately, most metamaterials, their applications, and metamaterials-based devices su˜er from a common problem: absorption loss in metal. Examples include but are not limited to a superlens, which resolution is highly sensitive to optical loss; negative index materials, in which light waves decay at the distances comparable to one wavelength; and optical cloak, whose performance can fail due to losses. All these materials and devices are discussed in di˜erent chapters of this book.