As a contribution to the special Kelvin symposium at ISEC, the author describes the very different contributions that Fahrenheit and Kelvin made to the development of temperature scales. He shows that Fahrenheit's approach was very literal and was not based on a fundamental approach, but nevertheless was the ultimate refinement of a tradition started in ancient Greece. Kelvin's approach on the other hand was a true departure from tradition and was born from fundamental considerations based on fresh developments in thermodynamics.