This chapter reviews the most common types of data available in health and examines administrative claims data that can be used to develop data-driven methods to address the high utilizer problem. Health care data systems are a systematic way to collect and process patient data from all stages of health care. Clinical researchers may also use biosensor data from mobile smartphones and wearable devices to monitor and manage a patient’s health and deliver better health care. Health care organizations have developed multiple coding systems to capture some of the most important dimensions of health care data: diagnoses, medical procedures, and medications. A well-organized and comprehensive set of procedure codes can classify the medical interventions in a standardized way, make it easier for doctors and patients to track and understand a patient’s medical history, and bill appropriately. Pharmaceutical codes, especially drug codes, are vital to drug dispensing and management as well as precise billing and controlled substance monitoring.