This book has been written with the aim of compiling from modern environments information that can be useful in the reconstruction of ancient environments. It is intended for all those interested in recognizing depositional environments. The study of sediments includes investigations of various aspects of sediments. This needs a study by standard methods. Methods of study have not been included, as many textbooks exist on the subject. However, the importance of various results obtained from such investigations has been discussed, as far as these results can be helpful in environ- mental reconstruction. Special attention is given to information that has accumulated during the last decades on the mode of genesis of various sedimentary features and their distribution in present-day environments. As far as possible, existing terminology has been used. How- ever, in several cases new simple groupings and classifications have been proposed. In making classification, generally, the form and shape of the features have been considered, so that they can be applied easily to ancient sediments. At the same time, the genesis of such features has been noted, and genetic names and their characteristics have been given for detailed work. The subject is so vast that several primary sedimentary features that have no direct bearing on environmental interpretation have been omitted. The subject is vast, and numerous publications are available.