Animal sentinel surveillance is a key component of public health risk assessment. While many species serve as animal sentinels, companion animals have an especially valuable role as sentinels because of their unique place in people's lives, with exposure to similar household and recreational risk factors as those for the people who own them. Dogs and cats can help in early identification of food contamination, infectious disease transmission, environmental contamination, and even bioterrorism or chemical terrorism events. Early detection, leading to early intervention, can minimize the impact of these adverse events on both animal and human health.