Results of Recent delta studies provide a lithogenetic model which is applicable to Middle Pennsylvanian rocks of the northern Appalachian Plateau. The model is a three-dimensional lenticular body composed mainly of detrital rocks which grade upward and landward from clays (shales) to sand and which is the result of deltaic progradation. These detrital sediments are completely or partially enclosed in a veneer of chemically precipitated or indigenously formed peats (coals), root-penetrated clays (seat rocks) or carbonate sediments (limestone or ironstones) which were deposited on the offshore front or on marginal portions of the delta or accumulated on the delta-plain surface when it was no longer receiving appreciable detrital influx. Lateral shift of sites of major detrital deposition, a phenomenon common in Recent deltas, results in an en echelon arrangement of progradational detrital wedges, a distinctive feature of the ancient Appalachian sediments. The primary differences between these ancient deltaic sediments and their modern equivalents seem to arise from limited detrital supply for ancient deltas and from the site of ancient delta building in shallow, narrow embayments on the relatively stable continental plate. This contrasts with modern deltas, most of which are prograding toward oceanic basins. 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.