Infection prevention and control programs in the United States have changed significantly since the mid-20th century. Much of this change was a result of the influence of professional and nonprofit organizations; government, regulatory, and accrediting agencies; and scientific research and publications. Other influences include increasing acuity of patients, aging of the population, complexity and location of treatment interventions, and the increasing move toward care in home/ambulatory settings. There are various models for infection prevention and control programs and standards for infection prevention professionals.  This chapter includes information on organizations influencing practice and the overall structure and function of infection prevention and control programs.