Diet selection is an important requirement for evaluating the effects of herbivores on their environments; this would increase understanding of plant-herbivore interactions and help to achieve optimal management strategies and profitable animal performance. The development of a sound understanding of diet selection will be a key to improving the management of pastures. Diet selection describes the decisions animals make with regard to the plant material (plant parts, plant species and patches) they choose. The aim of this book was to investigate how plants characteristics, chemistry and the nutritive value are relate to the diet selection patterns.