Spin and Flavor Contents of the Proton

After a brief review of the experimental results obtained in deep inelastic lepton-nucleon scatterings and the Drell-Yan processes and their implications for the spin and flavor contents of the nucleon, we suggest that those features, that are contrary to the expectations of the naive quark model, can all be accounted for in the chiral quark model of Georgi and Manohar. In our formulation of the chiral quark model, the $\eta ^{\prime }$ meson is seen to play an important role.