Investigation of the proton structure at the future Electron-Ion collider

The investigation of the proton internal structure in high energy scatterings has been one of the central subjects in basic science since quantum chromodynamics(QCD) was established as a fundamental theory of the strong interaction. A lot of knowledge has been accumulated in the past half century through the perturbative QCD analysis of experimental data. However, in spite of tremendous theoretical and experimental effort, a lot of mysteries still lie in the proton structure. In particular, the role of gluons inside the proton is leaving a lot of room for research. The measurement of the gluon spin performed by RHIC is one of the most important fundamental progresses made in the past couple of decades. Further investigation will be inherited by the next-generation EIC experiment. In this talk, I will review the current status of our understanding about the proton structure and discuss what we can do at the EIC.