Importance of TheoryTheories create a difference in healthcare. “In nursing, theories are systematic explanations of events in which constructs and concepts are identified; relationships are offered; and predictions are made to describe, explain, predict or prescribe practice and research. Without nursing theory, nursing activities and interventions are guided by routine, tradition, external authority, or hunches, or they may simply be random” (McEwen & Wills, 2014, 72). The foundation of nursing is rooted in theory. Through theory, nursing has become an independent, self-directed profession leading to innovations and evidence-based practice. The idea of ​​nursing theories stems from the extensive work of Florence Nightingale whose beliefs and values ​​were based on cleanliness, fresh air, sanitation, comfort, and socialization necessary for healing (McEwen and Wills, 2014). Each of the leading nursing theorists who have contributed to excellence in professional nursing practice embraces the four key concepts essential to nursing practice: person, environment, health, and nursing (Hood, 2010). This article aims to identify the importance of the theory in relation to Sister Callista Roy and her coping model. Importance of Nursing Theory to the Nursing Profession Nursing theories and models are like the lifeline of the nursing profession; Without theory, nursing will continue to depend on borrowed theories and principles that fail to capture the true meaning of nursing. Theories guide practice, making it more efficient and effective, and the ultimate benefit of applying theory in nursing is improved patient care (McEwen and Wills, 2014). Nursing contributes middle of paper ...... to life. References: Li-Lin, C., Hsing-Fang, K. and Shi-Fang, P. (2013). A nursing experience of applying Roy's adaptation model to a patient with laryngeal cancer [Chinese]. Tzu Chi Nursing Journal, 12(2), 91-101. McEwen, M. and Wills, E. (2014). Theoretical basis of nursing (4th ed.). Philadelphia, PA: Lippincott, Williams and Wilkins. Nayback, A. (2009). PTSD in the combat veteran: Using Roy's adaptation model to examine the combat veteran as a human adaptive system. Issues in Mental Health Nursing, 30(5), 304-310. doi:10.1080/01612840902754404 Parker, ME & Smith, MC (2010). Nursing theories and nursing practice (3rd ed.). Philadelphia, PA: FA Davis Company Yi-Wen, C., Ya-Wen, S., and Miin-Rong, H. (2013). A nursing experience of an amputee patient with peripheral arterial occlusive disease [Chinese]. Tzu Chi Nursing Journal, 12(1), 108-117.