The term "hard core" has been used extensively over the past 15 years to identify persons who drink and drive regularly, typically at high blood alcohol levels. This article discusses how the term arose and clarifies what it means, both as a concept and in practice. It describes the characteristics of hard core drinking drivers and estimates their contribution to drinking driver trips, arrests, and crashes. It summarizes current knowledge and recommendations on the most effective means to affect their behavior and reduce their drinking and driving.