Every year billions of animals, from housecats to racehorses to pythons, are treated by veterinarians. The use of veterinary science to treat the health of animals has a long history; for the past five centuries it has developed as our understanding of animals'' fundamental biology, pathology, and pharmacology has grown. Rapid global changes expected in the twenty-first century will require the profession to respond proactively, embracing new challenges andopportunities. James Yeates, Chief Veterinary Officer of the RSPCA, introduces the field of veterinary science, covering the history of its scientific and clinical aspects from early practices to recent challenges such as the outbreak of BSE and antibiotic resistance, and considering the differences between human medicine and veterinary medicine. Analysing the key roles played by diagnosis, treatment, and prevention with regard to the health of farm animals and pets, he relates this to wider aspectsconcerning public health, such as z
