Nursing theory is the term given to the boy of knowledge that is used to support nursing practice. In their professional education nurses will study a range of interconnected subjects which can be applied to the practice setting. This knowledge may be derived from experiential learning, from formal sources such as nursing research or from non-nursing sources. To speak of nursing theory is often difficult. Nursing is many things to many people. Most universally agreed upon is that Nursing is a science involving people, environment and process fueled by a vision of transcendence in the context of healthcare. It is interesting to note that 90% of all Nursing theories have been generated in the last 20 years. Many schools encourage students to formulate personal philosophies or mid-range theories of Nursing as part of their curriculum. Some might argue that this multiplicity of theory is detrimental to the practice and undermines common vision. Others would say that the nature of the young science is sufficiently far reaching to require such tactics in order to elicit true consensus.