This book has three main aims: (1) To provide an easy-to-understand explanation of the basic theories of molecular vibrations and the relationship between molecular vibrations and spectra - infrared and Raman (2) To introduce spectrum-simulation methods based on the latest developments in quantum-chemical calculations, (3) To show examples of analyses of the structure-spectrum correlation for basic molecules, polymers, and crystals. In this book, the authors not only present valuable basic knowledge described in well-known classics in the fields of molecular spectroscopy, structural chemistry, and quantum chemistry, but also provide information on the up-to-date methods for performing todays research, so that young students and researchers who wish to do something in the field of infrared and Raman spectroscopy can acquire a minimum amount of knowledge needed for their research.