Quantum field theories (QFT) and the renormalization-group (RG) theory can be used to describe very different physical phenomena, such as fundamental interactions and critical phenomena in statistical and quantum systems. In my research activity, I have pursued both fields of study, using QFT and RG as main frameworks.  In particular, I have investigated non-perturbative aspects of the strong interaction theory, i.e. quantum chromodynamics (QCD), and critical phenomena in several (classical and quantum) physically interesting systems, from transitions in liquids and He4 to more complex systems, such as disordered and frustrated systems, quantum transitions in high-Tc superconductors and cold-atom systems, etc.