The aim of this course is to present and show the potentiality of the archetypical click reactions (CuAAC, Bertozzi copper free click chemistry, Staudinger ligation, SuFex, Thiolo-ene reaction) in different areas of research such as drug discovery, bioconjugation, in vivo imaging. In the first part, the molecular mechanisms of these reactions will be presented and discussed, while in the second part of the course will be presented real applications of these techniques.