Book excerpt: This book deals mainly with the results of the authors' research devoted to both the study of the transport equation (the linear Boltzmann equation) and its applications in X-ray tomography. The introduction gives an outline of the book and deals with certain aspects of the methodology. The first part of the book is devoted to the investigation of known and new problems for the stationary transport equation of a general form. New problems are treated as problems of tomography. The second part deals with the monoenergetic transport equation. This book will be of interest to specialists in transport theory and tomography.