Size Exclusion Chromatography (SEC) is the separation of mixtures based on the molecular size of the components. Separation is achieved by the differential exclusion or inclusion, within the packing particles, of the sample molecules as they pass through a porous-particle stationary phase. The principle feature of SEC is its gentle non-adsorptive interaction with the sample, enabling high retention of biomolecular activity. For the separation of biomolecules in aqueous systems, SEC is referred to as gel filtration chromatography (GFC), while the separation of organic polymers in non-aqueous systems is called gel permeation chromatography (GPC).

Size exclusion chromatography is used primarily for analytical assays and semi-preparative purifications. It is typically not used for process scale work due to its lack of binding capacity.