The experience of energy and fatigue are essential features of life that influence on peoples daily activities, bodily movements, relationships, and disability. This research project was designed to gain knowledge with respect to the experience of energy and fatigue in various populations by different research methods. First, there was a need to explore the concept of energy. The next step was to measure fatigue in the general population. Finally, fatigue in a population of patients with Multiple sclerosis (MS) and the relationship between HRQoL (including vitality), and patients overall perception of MS severity and change in MS severity were examined. The study showed that fatigue was characterized by four dimensions of the feeling of energy, i.e. quality, energy level, energy pattern and distress. The study has confirmed previously documented knowledge that fatigue occurs commonly in MS patients and is perceived as a major problem. Therefore, health professionals who care for individuals with MS should always consider fatigue as one of these patients potential problems.