Publisher Summary This chapter discusses the compaction of argillaceous sediments. It incorporates mathematical developments of compaction models, a treatise of stresses in sediments, and basic concepts of fluid flow through porous media. The importance and inherent complexity of the chemistry of interstitial fluids and the behavior of these solutions during compaction is highlighted in the chapter and is thoroughly treated based on theoretical concepts, experimental data, and actual field observations. Compaction of sediments under the influence of a vertical monotonic loading has long been a well-documented geologic phenomenon. This mechanism appears to be a likely candidate for creating an environment conducive to the formation of high fluid potentials in sediments having low permeability. In most sedimentary rocks, connate water is the predominant interstitial fluid. The degree of expulsion of water from the pore space by compaction provides a foundation for developing interrelationships between abnormal formation pressures, velocity of fluid expulsion, and pressure profiles through the sedimentary column. The first basic premise in a compaction model development is that the rate of gravitational compaction of sediments of a depositional basin is limited by the low permeability of the argillaceous members.