This book is intended to meet the needs of those using the technique of near infrared spectroscopy routinely. It therefore contains only sufficient detail to provide an understanding of how NIR works so that readers can approach their applications. A new chapter has been included in this edition in recognition of the growing importance of on-line instrumentation. The other most significant advance since 1986 has been in calibration mathematics. The growth in popularity of monochromator-based instruments has led to the development of commercially-available software packages for NIR calibration by principal components analysis and partial least squares. This edition describes these techniques in more detail.