Chiral symmetry and its breaking

In addition to fundamental symmetries playing a crucial role for establishing the Standard Model of fundamental interactions, approximate symmetries provide essential insight into the respective phenomena and shed light on the underlying physics. Here we give a brief pedagogical introduction to chiral symmetry as an approximate but still rather accurate symmetry of strong interactions and its spontaneous breaking in the vacuum of Quantum Chromodynamics. Special attention is paid to a microscopic picture of this phenomenon and understanding a dual nature of the chiral pion that is the Goldstone boson related to spontaneous breaking of chiral symmetry and the lowest pseudoscalar quark-antiquark state in the spectrum of hadrons simultaneously.