Dorothea Orem developed her Theory of Self Care, which has three main concepts: self-care, self-care deficit, and nursing systems. Self-care refers to one's ability to perform activities to maintain health. Self-care deficit occurs when one is unable to meet self-care needs due to limitations. Nursing systems are the nurse's actions to help meet a person's self-care demands based on their level of self-care ability or deficit. Orem's theory is applied in nursing practice through the nursing process, with self-care informing assessment/evaluation, self-care deficit guiding diagnosis, and nursing systems relating to interventions.