Maslow in the Context of Leadership and Employee Engagement by Shea Heaver
In 1943 Abraham Maslow first brought his Hierarchy of Needs theory to the world in which he looks at what motivates individuals.
He claimed that people are motivated by things and circumstance that range from basic survival up through up to the ability to reach and achieve one's full potential.
That sounds like something which could be applied in the workplace to elevate employee's motivation from simply being there to get a paycheck all the way up to performing at a very high level...
...and actually, enjoy doing it.