It has been known for over 20 years that the x-ray emission from black hole binaries displays quasi-periodic oscillations (QPOs) . Although this is a very well studied phenomenon, there is still no consensus in the literature as to the physical process driving this periodicity. I describe a model that associates the QPO with relativistic precession of the inner regions of the accretion flow and show that this predicts the observed evolution in both QPO frequency and spectral state. In addition, the model also reproduces the correlation between QPO frequency and flux which is observed to hold on short time scales. I then go on to describe other more subtle properties of the model which we may soon be able to test by studying the time resolved behaviour of the iron line.