Knowledge is power. Expert power is derived from possessing knowledge or expertise in a particular area. Such people are highly valued by organizations for their problem solving skills. People who have expert power perform critical tasks and are therefore deemed indispensable. The opinions, ideas and decisions of people with expert power are held in high regard by other employees and hence greatly influence their actions. Possession of expert power is normally a stepping stone to other sources of power such as legitimate power. For example, a person who holds expert power can be promoted to senior management, thereby giving him legitimate power.