Book excerpt: The first part of a comprehensive overview of fundamental optical properties of III-nitride semiconductors. All optoelectronic applications based on III-nitrides are due to their unique optical properties and characterizations of III-nitrides. Much information, which is critical to the design and improvement of optoelectronic devices based on III-nitrides has been obtained in the last several years. This is the first of a two part Volume in the series Optoelectronic Properties of Semiconductors and Superlattices. Part I begins with time-resolved studies of semiconductors and moves on to the emphasis on time-resolved photoluminescence of nitride materials and device technology and focuses on Raman studies and properties of III Nitrides. This unique volume provides a comprehensive review and introduction of the defects and structural properties of GaN and related compounds. This would be excellent for newcomers to the field and is a stimulus to further advances for experienced researchers.III-Nitride Semiconductors: Optical Properties Part I combines contributions from active experts in the field with diverse backgrounds. This book provides a very important step in advancing the state of research and device development in the field of III-nitride materials.