More than 99% of the visible matter in the universe is the nucleons (protons and neutrons). Their internal structure is mostly governed by the strong interaction. Understanding their internal quark-gluon structure is in the frontier of modern physics research. Worldwide efforts have led to numerous discoveries and surprises, but major challenges still remain. An overview of the progress will be presented with a focus on the recent studies of the nucleon mass, spin and 3D structure. Selected highlights of the recent results from Jefferson Lab will be presented. Plan for future physics programs will be discussed.