A review of liquid chromatography (LC) techniques for the subfractionation of complex protein mixtures into ''subproteomes'' is presented. Fractionation of protein mixtures into general subclasses based on physical, chemical, and biological attributes of proteins is an effective way of classifying and characterizing complex proteomes. Classical chromatographic techniques, such as reverse-phase, ion-exchange, and size exclusion chromatography (SEC) are discussed, as well as a variety of affinity chromatography techniques such as immobilized metal affinity chromatography (IMAC) and lectin affinity chromatography. Applications of these methods to proteomic endeavors are highlighted. Multidimensional chromatography methodologies are examined for combining orthogonal chromatographic formats interfaced with mass spectrometric (MS) detection. The versatility of liquid chromatography for proteomic analysis makes LC a valuable tool for the protein characterization of living systems.