This book is all about integrated ring resonators made out of optical waveguides in various materials for different applications. Integrated ring resonators are used to build optical—lters, lasers, sensors, modulators, d- persion compensators, just to name a few. The book covers the range from simulation of various ringresonator configurations to the fabrication processes currently used, to the description of the application of integrated ring re- nator in various fields. The book presents a summary of the activities in this field form the past to the current state of the art giving several examples. The book is written for students, graduates, professionals, academics and industry working in this exciting field. The examples in literature used in this book have been collected over four years, categorizing the different examples into what are now the chapters of this book. Integrated ring resonators have been and still are a fascinating class of devices and have interested me since the beginning of my PhD in 1999. I am therefore grateful to the entire integrated ring resonator community for providing me with exciting and cutting edge research material which e- bled me to write this book. Due to the enormous amount of publications in this attractive field, I hope, that I was able to refer to most of the work done so far and would be thankful if I was made aware of any “undiscovered” work. As research on integrated ring resonators is on going, I would also be happy to receive material for my database which can then of course be included in further publications.