Publisher Summary This chapter describes the fundamental aspects of gel chromatography as they comprise a set of analytical techniques that a protein chemist may use. The unifying principles that underlie these techniques have been a major focus of interest. The chapter focuses on the two fundamental principles that underlie the use of gel chromatographic systems as analytical tools in protein chemistry: (1) partition coefficients depend on molecular size and shape in contrast to surface or charge properties. (2) Gel columns are linear chromatographic systems and can, therefore, be used for the analysis of nonlinear molecular phenomena such as those occurring in chemically reacting multicomponent systems. Although deviations from these two principles of ideal behavior are almost always present, their magnitude is almost always small. In addition, it is evident on both theoretical and experimental grounds that the group of techniques based on the partitioning of molecules into porous gel networks constitutes an extremely versatile and useful array of analytical tools for the studies of protein systems. It may be expected, therefore, that the application of these techniques will be extended to a much wider group of experimental systems.