Gel permeation chromatography (GPC), also known as size-exclusion chromatography (SEC ), is a chromato- graphic technique that employs specialized columns to separate natural and synthetic polymers, biopolymers, or proteins on the basis of their size. GPC is the most widely used technique for the analysis of polymers, in relation to other techniques of molecular weight (MW) measurement; the analysis is very fast (compared to older techniques) and can be carried out in a couple of hours. It can be used for samples soluble in organic and aqueous eluents, and for MWs from approximately 100 to several million daltons (Da). With GPC, it is also possible to obtain the MW of polymers that are soluble only at high temperatures. Be- sides, in contrast to traditional techniques, it yields all MW averages and the molecular weight distribution (MWD).