Electromagnetism, quantum mechanics, statistical mechanics, molecular spectroscopy, optics and radiation form the foundations of the field. On top of these rest the techniques applying the fundamentals (e.g. Emission Spectroscopy, Laser Induced Fluorescence, Raman Spectroscopy). This book contains the basic topics associated with optical spectroscopic techniques. About 40 major sources are distilled into one book, so researchers can read and fully comprehend specific optical spectroscopy techniques without visiting many sources. Optical diagnostics are widely used in combustion research. Ideas first proposed here are now applied in other fields, including reacting flows for materials production (CVD reactors, oxidation reactors and some plasma work), atmospheric sensing, measuring constituents of exhaled human breath (to indicate stress in airway passages and the lungs and hence,e.g., provide a very early indicator of lung cancer). Researchers not formally trained who apply spectroscopy in their research need the detail in this book to ensure accuracy of their technique or to develop more sophisticated measurements. Time is valuable and future research will benefit. Learning 'on the fly' can involve direct information on a specific diagnostic technique rather than gaining the background necessary to go into further depth.