Working with proteins has always been a big challenge, yet an amazing adventure, specially when at the end of the day new scientific information could be collected, and be critical to deep understand the structure and function of the different proteins. The present book gives more attention to the ATPase, and the conformational changes occurring upon binding of the b-dimer to the F1-part of the whole enzyme FoF1-ATPase. The main biophysical method that was used to achieve the goals of this study is the electron spin resonance spectroscopy.