Focusing on optical imaging problems, applications, and theory, this book describes progress in optical tomography. The text consists of several self-contained chapters with references written by pioneers and experts in the theoretical aspects of optical tomography and nonlinear imaging in general. The first chapter introduces the theoretical problem of optical tomography as it is relevant to applications in biomedical imaging. Each subsequent chapter addresses a particular technique that has been applied to tackle the problem of instability in optical tomography. The last three chapters summarize the state of the art and address the future of the field.