This book contains the proceedings of the XIth International Symposium on Ruminant Physiology. The papers address ruminant comparative physiology, the rumen ecosystem and metagenomics, nutrient digestion and absorption, methanogenesis, tissue metabolism and gene expression, pregnancy, lactation and growth, adaptation to heat-stress, nitrogen use, nutrition and reproduction, nutrition and welfare and nutrition for sustainable ruminant production. These topics are in line with the current challenges for animal breeding: production efficiency, meat and milk quality, environment (greenhouse gases, nitrogen use), animal welfare and health. The contributions come from research teams in 49 countries of all continents, showing a world-wide interest in ruminant nutrition and physiology. They show the latest techniques and results on ruminant nutrition physiology, including fundamental and integrative approaches, presented in the book on the following sections: (1) Digestion and absorption, (2) Metabolism and hormonal regulations, (3) Nutrition and reproduction, (4) Nutrition and welfare. Proceedings from past ISRP symposia have had a major influence on research and teaching in animal science over the years. Without a doubt, this book, which is of interest to all professionals and researchers who are concerned with ruminant nutrition and physiology, will contribute to this fine tradition.