In addition to their primary function in food production, pasture-based animal production systems contribute to the management of climate change and landscape diversity, implications for biodiversity and the socio-economic sustainability of agriculture, and the ethics, quality and safety of natural animal products. In the more productive pasture-based systems, the challenge is to combine a high animal productivity with high pasture utilization and a moderate use of fertilizers, all these factors contributing to reducing the carbon footprint of the milk and meat produced, water pollution, reliance on bought-in concentrate and sensitivity to input costs volatility (Benoit and Laignel, 2010; Dillon et al., 2005). These economic and environmental concerns have renewed interest in increasing the use of grass/legume swards. In the more extensive grassland systems, farmers have to manage larger fl ocks on larger and more diversifi ed areas and pastures, and to reconcile production with environmental objectives such as maintaining open landscapes and contributing to landscape biodiversity. The lower grazing pressure is favourable to pasture structural heterogeneity and therefore to pasture biodiversity. Facing this diversity in grassland systems, management objectives and forage resources, the scientific challenge is to provide an understanding of the biological principles that govern system behaviour in a broad range of conditions. The objective of this chapter is to give an overview of the state of knowledge on the infl uence of vegetation characteristics on foraging strategy and ingestive behaviour in animals grazing both temperate and tropical swards.