In this chapter, we will address the potential applications of negative refraction in
artificial periodic media. Different approaches will be considered depending on the targeted
wavelength operation from microwaves down to optics. First, physical concepts to create such
an abnormal propagation regime will be described: (i) negative permittivity and negative
permeability engineering in patterned metallic or metallo-dielectric structures namely
metamaterials and (ii) band structure engineering in full dielectric structures namely photonic
crystals. Second, practical examples of real devices will be given, starting from negative
refraction evidence in a two dimensional prism in microwaves, backward wave propagation in a
periodically loaded transmission line to end with subwavelength focusing by a photonic crystal
slab for optical waves. In the third part, other exciting properties beyond negative refraction will
be evoked with the design of hyperlenses and cloaking devices.
