A clinical nurse specialist (CNS) is an advanced practice nurse who can provide advice related to specific conditions or treatment pathways. According to the International Council of Nurses (ICN), an Advanced Practice Nurse is a registered nurse who has acquired the expert knowledge base, complex decision-making skills and clinical competencies for expanded practice, the characteristics of which are shaped by the context and/or country in which s/he is credentialed to practice. Clinical Nurse Specialists are registered nurses who have had graduate level nursing preparation at the master's or doctoral level as a CNS. They are clinical experts in evidence-based nursing practice within a specialty area, treating and managing the health concerns of patients and populations. The CNS specialty may be focused on individuals, populations, settings, type of care, type of problem, or diagnostic systems subspecialty. CNSs practice autonomously and integrate knowledge of disease and medical treatments into the assessment, diagnosis, and treatment of patients' illnesses. These nurses design, implement, and evaluate both patient–specific and population-based programs of care. CNSs provide leadership in the advanced practice of nursing to achieve quality and cost-effective patient outcomes as well as provide leadership of multidisciplinary groups in designing and implementing innovative alternative solutions that address system problems and/or patient care issues. In many jurisdictions, CNSs, as direct care providers, perform comprehensive health assessments, develop differential diagnoses, and may have prescriptive authority. Prescriptive authority allows them to provide pharmacologic and nonpharmacologic treatments and order diagnostic and laboratory tests in addressing and managing specialty health problems of patients and populations. CNSs serve as patient advocates, consultants, and researchers in various settings.