Nucleons (protons and neutrons) are the building blocks of atomic nuclei and are responsible for more than 99% of the visible matter in the universe. Despite decades of efforts in studying the structure of the proton, there are still interesting puzzles surrounding the proton such as its spin and the charge radius. The mass of the proton is another fascinating topic as most of the proton mass has little to do with the mass of its constituents. In this talk I will review some recent advances in the study of the nucleon structure, and then discuss future studies with an Electron-Ion Collider to be built at the Brookhaven National Laboratory in the coming decade.