This lecture covers the main concepts of Quantum Chromodynamics (QCD), including the theory behind QCD, the local gauge principle, color in QCD, color confinement, gluons, color singlets, meson and baryon color wave-functions, and the implications of color confinement. It also discusses the discovery of the gluon, the running coupling constants in QCD and QED, and the pseudorapidity coverage in CMS and LHCb detectors.