  We review the current status and future prospects on the subject of flavor
structure of the nucleon sea. The flavor structure of the nucleon sea provides
unique information on the non-perturbative aspects of strong interactions
allowing stringent tests of various models on the partonic structures of the
nucleons as well as lattice QCD calculations. The scope of this review covers
the unpolarized, polarized, and the transverse-momentum dependent sea-quark
distributions of the nucleons. While the main focus of this review is on the
physics motivation and recent progress on the subject of the nucleon sea, we
also discuss future prospects of addressing some outstanding issues on the
flavor structure of the nucleon sea.
