The purpose of surveillance is to provide timely and relevant information to allow early warning and inform policy makers for rapid response to reduce the spread and mitigate the impact of disease. This practical handbook about surveillance is intended to be used mainly by Veterinary Services or other Competent Authorities, their staff and experts as a tool for strengthening the design, implementation and evaluation of surveillance systems for diseases of relevance for terrestrial animals in their country. The book reflects the contribution of experts in surveillancemethodology from across the world. Recognising the diversityof animal husbandry and other situations in Member Countries and the dynamic nature of animal health, the document presents a flexible framework for integrating surveillance approaches that meet both national and international needs and that should remain relevant as surveillance evolves to embrace new challenges and opportunities. Veterinary Services complying with OIE standards on quality are a cornerstone for effective passive and active surveillance activities, as well as efficient public-private partnerships between official and private veterinarians and animal owners,hunters and rangers in conservation areas.