Vitamin A plays a key role among the vitamins essential for healthy growth and development. Vitamin A deficiency disorders (VADD) are therefore an important part of general malnutrition that in the majority of cases leads to failure to thrive and underweight. Moreover, apart from adverse effects on health and survival in general, VADD can also lead to blindness, called xerophthalmia, and are also frequently accompanied by various infections. Last but not least, it has become evident that even mild degrees of VAD (and all other forms of nutritional deficiencies) have important adverse implications for health and are thus much more widespread than previously assumed. This publication systematically covers detailed and up-to-date information on every relevant aspect of VADD, with particular emphasis on providing an outline of their setting, nature, and significance. In addition to cutting-edge scientific information, the latest available data on the global occurrence of VAD from the World Health Organization is also included.