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Relativistic Dirac and Weyl fermions were extensively studied in quantum field theory. Recently they emerged in the nonrelativistic condensed-matter setting as gapless quasiparticle states in some types of crystals. Notable examples of 2D systems include graphene and surface states in topological insulators such as **Bi_2Se_3**. Their 3D reincarnation is Dirac and Weyl semimetals that were recently discovered experimentally. Most of the research has been focused on their topological properties and electron transport. However, their optical properties are no less exciting. Moreover, optical phenomena can provide unique insight into fascinating physics of these materials. I will discuss several examples illustrating this point. They include: plasmons and normal modes in Weyl semimetals, nonlocal optical response of graphene and topological insulators, and optical properties of chiral Dirac/Weyl fermions in a quantizing magnetic field.