The present book is based on experiences that the senior author gained from 1945 to 1983 as an employee of the Franco-German Research Institute in Saint Louis, and that the junior author gathered from 1971 to 1981 as a staff member of the Institute for Fluid Mechanics and Fluid Machines at the University of Karlsruhe. It aims to fulfill a request made by listeners of both authors' lectures at the University of Karlsruhe. There has been a consistent demand for a book that not only provides a thorough introduction to the key areas of optical flow measurement technology but also offers a comprehensive overview of the entire field and insights into recent developments. Some subfields have already been summarized in previous reports.