This book provides a comprehensive understanding of the fundamentals of thin-film PV devices as well as practical direction on how to perform optical modeling and simulations of thin-film PV structures. The authors include numerous real examples of using simulations with developed models in order to study and design novel approaches to light management. The first part of the text presents fundamentals and optical modeling approaches. The second part focuses on simulations based on one- and two-dimensional optical models. The authors also explore advanced and novel optical concepts of PV devices.