Carotenoid are ubiquitous compounds serving a series of functions that make them special. Thus, they are regarded as essential compounds for life mainly due to the different roles they perform in photosynthesis as we currently know it. For many years, the nutritional relevance ot carotenoids was due to some of them exhibiting vitamin A activity, although the interest in these pigments has expanded dramatically in the last years owing to a large variety of surveys that seem to indicate that they are antioxidant and may be beneficial for the prevention of several chronic non-transmissible human diseases, albeit there is some controversy in this regard. In any case, it is clear that the different functions and effects attributed to these isoprenoids stem from their physical and chemical properties, the latter being due to their chemical structure. Due to the diverse benefitial actions carotenoids are responsible for and, above all, to their nutritional importance, the main objective of this review is to describe such features, whose knowledge is indispensable to have a holistic view of the different roles they play and for the design of new studies.