  This paper presents a first-principle and global perspective of
electromagnetic chirality. It follows for this purpose a bottom-up
construction, from the description of chiral particles or metaparticles
(microscopic scale), through the electromagnetic theory of chiral media
(macroscopic scale), to the establishment advanced properties and design
principles of chiral materials and metamaterials. It preliminarily highlights
the three fundamental concepts related to chirality -- mirror asymmetry,
polarization rotation and magnetodielectric coupling -- and points out the
nontrivial interdependencies existing between them. The first part (chiral
particles) presents metamaterial as the most promising technology for
chirality, compares two representative particles involving magnetoelectric
coupling, namely the planar Omega particle and the twisted Omega or helix
particle, and shows that only the latter is chiral, and finally links the
response of microscopic particles to that of the medium formed by arranging
them according to a subwavelength lattice structure. The second part
(electromagnetic theory) infers from the previous microscopic study the chiral
constitutive relations as a subset of the most general bianisotropic relations,
derives parity conditions for the chiral parameters, computes the chiral
eigenstates as circularly polarized waves, and finally shows that the circular
birefringence of these states leads to polarization rotation. The third part
(properties and design) introduces an explicit formulation of chirality based
on spatial frequency dispersion or nonlocality, analyzes the temporal frequency
dispersion or nonlocality of chiral media, and finally provides guidelines to
design a practical chiral metamaterial.
