This book is intended to give an introduction to sedimentology and petroleum geology at undergraduate level. These two subjects have been treated together because of the close links between sedimen­ tology as an academic dicipline, petroleum geology, which is the application of sedimentology, and a number of other aspects of petroleum exploration and production. The oil industry ist by far the most important employer of sedimentologists and the lively interaction that takes place between the academic community and the research laboratories and exploration departments of the oil industry has been very fruitful for both parties. Our knowledge of sedimentary basins now depends to a very large extent on data obtained by commercial petroleum exploration. Studies of actual rocks in outcrops, particularly if they are extensive, will always be important for sedimentologists, but subsurface data like seismic sections and well logs provide us with in much information on the three-dimensional distribution of facies that we could not otherwise obtain. Subsurface techniques are certainly important for pe­ troleum geologists, but also other sedimentologists should be able to use subsurface data. I have therefore included elementary intro­ ductions to the use of well logs and seismic methods in this book, with fundamentals of external controls on sedimentation such as basin subsidence and sea level changes. I have tried to present the state of knowledge at this level without referring to the original research papers except when specific data are quoted or used in illustrations.