Factors controlling depositional processes and products are analyzed for three of the world’s major river-delta systems; the Mississippi, Ganges-Brahmaputra, and Mekong. Despite variations in amount of available data it is apparent that these three river systems have developed deltas displaying varied geomorphic form which reflects differences in depositional processes and products. Such contrasts are of interest to the geologist attempting to compare ancient with modern deltaic environments. Four basic factors control and influence delta formation: (1) river regime, mainly particle size and quantity of material transported by a river to its delta and variations in these properties during seasonal fluctuations in flow ; (2) coastal processes, essentially the influence of waves, tides, and currents on the seaward margins of the deltaic environment; (3) structural behavior and the relation of sea level to the depositional site ; for example, is the delta prograding across a stable platform, or is the area subsiding contemporaneously with sediment deposition, and are these changes occurring in a background of stationary, rising, or falling sea level ; and (4) climatic factors, particularly those that affect vegetation within the delta. Although all factors play some role in producing differences among these three deltas, certain ones appear to be more influential in producing some of the more obvious variations. The Mississippi delta area is characterized by rapid subsidence, primarily through sediment compaction, and its deposits are subject only to minor modification by coastal processes. Several overlapping deltas have formed during the Recent as sedimentation sites have undergone rather systematic lateral shifting during progradation. Rapid burial and only minor influence by coastal processes preclude the development of extensive laterally continuous sand bodies, although lenticular channel fill and beach sands are present. The Ganges-Brahmaputra delta is also tectonically controlled but by Quaternary faulting as well as by subsidence through sediment compaction. River courses and sedimentation sites have shifted erratically in response to intermittent structural change. In contrast to the Mississippi, coastal processes are much more important, and high tides in the Bay of Bengal have created an extensive tidal plain of predominantly finegrained sediments. Laterally continuous sands are not typical of this delta. The Mekong has created a single delta system which has prograded across an essentially rigid platform. Contemporaneously, coastal processes (tides, waves, and currents) have reworked the delta front, creating sand beaches which merge laterally to form widespread sheet sands in the deltaic plain. This volume was based on a symposium, Deltaic Sedimentation, which was held at the AAPG/SEPM Annual Meeting in New Orleans, Louisiana on April 1965. Many geologists have become involved in studies of deltaic sediments and sedimentation processes. Some of the papers in this volume are based on detailed local studies of modern deltaic sedimentary sequences, on processes of deposition, and on physical and biological characteristics of the deltaic environments.