Faye Glenn Abdellah developed the "Twenty-One Nursing Problems" which categorized common patient health issues and nursing responsibilities into 21 problems. These problems fall under basic needs, sustaining care needs, remedial care needs, and restorative care needs. Abdellah believed nursing care should be based on research and solving identified problems. Her theory transformed nursing from a disease-focused to a patient-centered approach and provided a framework for assessing patients, planning care, and evaluating outcomes. While strong in orienting nursing actions, the theory lacks emphasis on client-defined goals and could be more holistic. Overall, it guided the development of evidence-based, problem-solving nursing care.