Official Twitter of the American Association of Critical-Care Nurses: A Community of Exceptional Nurses. Tag us @AACNme #AACN. https://t.co/sbJET277OU AACN is the largest specialty nursing organization in the world, joining together the interests of more than 500,000 nurses who are charged with the responsibility of caring for high acuity and critically ill patients and their families. AACN Certification Corporation drives patient health and safety through comprehensive credentialing of acute and critical care nurses, advancing practice consistent with standards of excellence.