The Mississippi delta complex is one of the largest and probably best known of the world’s major delta systems. Its subaerial surface, the Mississippi deltaic plain, extends from an apex at the mouth of the Mississippi alluvial valley to a base of 200 miles along the Louisiana coast. Underlying this plain and the adjacent continental shelf and slope is a huge mass of late Quaternary river-mouth deposits which makes up the deltaic complex. These sediments occupy a seaward deepening troughlike depression in the underlying surface that developed contemporaneously with deposition and which is localized to the depositional area. Downwarping of this segment of the continental margin, together with the eustatic rise in sea level during late Quaternary time, was sufficient to accommodate the great thickness of deposits which reaches a known maximum of about 1,000 feet underlying the continental shelf at the seaward limit of control. Beneath the deltaic plain and inner shelf, the late Quaternary deposits consist of a thick onlapping sequence grading upward from basal fluvial and strand-plain sands and gravels to deltaic and marine silts and clays with local sand lenses. This sequence is overlain by a thinner series of offlapping deltaic sands, silts, and clays exposed on the deltaic plain. The onlapping sequence records the eustatic rise of the sea from its last low stand, whereas the offlapping sequence represents progradation after the sea reached its present level some 3,500 to 4,000 years ago. At that time, the Gulf of Mexico shore coincided approximately with the present coastwise Pleistocene-Recent contact and subsequently has been advanced far seaward by construction of the deltaic plain, in building this plain, the Mississippi River occupied and abandoned two courses and several deltas prior to establishing the present course and active delta. In order of decreasing age, these are the Teche, St. Bernard, Lafourche, Plaquemines-modern, and modern birdfoot deltas. Except for the birdfoot delta, which is advancing into deep water of the continental slope, each of the deltas was built forward onto the shallow inner margin of the continental shelf. Sediments delivered through leveed distributaries were deposited in a variety of environments. Most of the sand was laid down in distributary-mouth bars of the delta front. Silts and clays were swept further seaward into the marine prodelta zone and during floods into swamps, brackish marshes, bays, lakes, and channels of interdistributary and delta-flank depressions of the deltaic plain. Thick accumulations of peat and organic muck, which kept pace with subsidence during and following delta building, now cover these earlier formed deposits. Both the shallow-water deltas and the active deepwater birdfoot delta are characterized by distinctive facies which are readily recognized by their lithologic, faunal, and geometric features. 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.