AbstractGel filtration (GF) chromatography separates proteins solely on the basis of molecular size. Separation is achieved using a porous matrix to which the molecules, for steric reasons, have different degrees of access‐‐i.e., smaller molecules have greater access and larger molecules are excluded from the matrix. Hence, proteins are eluted from the GF column in decreasing order of size. This unit describes the experimental theory behind gel filtration and contains many useful tables listing the properties and characteristics of currently available matrices.