All practicing veterinarians working with herds and flocks are consulted on animal population problems. These problems may reflect diseases with high morbidity or high mortality rates or other events that impair productivity. In either case, the ultimate goal of the veterinary practitioner is to control the problem and to prevent its recurrence, while keeping the cost of interventional strategies at a minimum. A systematic approach to outbreak investigation is a successful means of achieving the objectives of control and prevention. This approach, although described in a stepwise manner, is not meant to be rigidly applied, but rather should serve as a guide for the investigator. Structured investigations facilitate the efforts of both inexperienced and veteran practitioners. Otherwise, experienced practitioners might develop biased conclusions owing to a specific area of expertise or interest, or because of the influence of previous experience with similar cases. The veterinarian should assume a leadership role in outbreak investigation and should not hesitate to consult with specialists if needed. Although all population problems do not warrant a thorough investigation, the systematic approach just presented, when used for complex problems, increases the probability of establishing definitive, accurate conclusions.