The Hersey-Blanchard Situational Leadership Theory, is a leadership theory conceived by Paul Hersey, a professor who wrote a well known book Situational Leader and Ken Blanchard,well know author of The One Minute Manager, while working on the first edition of Management of Organizational Behavior (now in its 9th edition) . The Theory was first introduced as "Life Cycle Theory of Leadership" . During the mid 1970's "Life Cycle Theory of Leadership" was renamed "Situational Leadership theory" . In the late 1970s/early 1980s the authors both developed their own Models using the Situational Leadership theory; Hersey - Situational Leadership Model and Blanchard et al. Situational Leadership II Model. The fundamental underpinning of the Situational Leadership Theory is that there is no single “best” style of leadership. Effective leadership is task-relevant, and the most successful leaders are those that adapt their leadership style to the Maturity (“the capacity to set high but attainable goals, willingness and ability to take responsibility for the task, and relevant education and/or experience of an individual or a group for the task) of the individual or group they are attempting to lead/influence. That effective leadership varies, not only with the person or group that is being influence, but it will also depend on the task, job or function that needs to be accomplished. The Hersey-Blanchard Situational Leadership Theory rests on two fundamental concepts; Leadership Style and the individual or group's Maturity level.