More than twenty years after the idea of this Carotenoids book series was first discussed, we finally reach the end of the project with Volume 5, which covers the functions and actions of carotenoids in human nutrition and health. In 1971, in Isler’s book Carotenoids, functions of carotenoids and vitamin A were covered in just two chapters. Now, thanks to technical developments and multidisciplinary approaches that make it possible to study functional processes in great detail, this subject is the most rapidly expanding area of carotenoid research, and occupies two full volumes, Volumes 4: Natural Functions and 5: Nutrition and Health. Although Volume 5 can be used as a single stand-alone volume, the two were planned as companion volumes to be used together. To understand the mechanisms of functions and actions of carotenoids, including how carotenoids may be involved in maintaining human health, requires understanding of the underlying principles, which are presented in the first part of Volume 4. The general philosophy and strategy of the series, to have expert authors review and analyse critically a particular topic and present information and give guidance on practical strategies and procedures is maintained in Volumes 4 and 5. It is also the aim that these publications should be useful for both experienced carotenoid researchers and newcomers to the field.