In 8 years after the publication of the first version of this book, the rapidly progressing field of inverse problems witnessed changes and new developments. Parts of the book were used at several universities, and many colleagues and students as well as myself observed several misprints and imprecisions. Some of the research problems from the first edition have been solved. This edition serves the purposes of reflecting these changes and making appropriate corrections. I hope that these additions and corrections resulted in not too many new errors and misprints.