Quark Asymmetries in the Proton

We review recent experimental and theoretical developments in the study of the sea quark structure of the proton. In the light quark sector, we analyse the recent pp and pD Drell-Yan data from the E866/NuSea experiment at Fermilab, and their implication on the d̄/ū asymmetry in the proton. The current status of the strange content of the proton, including the possible difference between strange and antistrange quark distributions and strangeness form factors, is updated. Finally, we point out the implications of the possible non-symmetric charm and anticharm distributions in the nucleon for HERA event rates at large x and Q.