Atomic force microscopy (AFM) can be used to characterise several aspects of the surface degradation and reinforcement mechanisms of zirconia based ceramics, such as crack propagation, martensitic relief formation, grains pull-out and transformation toughening. AFM can also be used to quantify precisely the transformation and provide reliable parameters for long term degradation prediction. In particular, the tetragonal to monoclinic (t-m) phase transformation of zirconia has been the object of extensive investigations of the last twenty years, and is now recognised as being of martensitic nature. New strong evidences supporting the martensitic nature of the transformation are reported here. These observations, considering their scale and precision, are a new step toward the understanding of the t-m phase transformation of zirconia and related degradation mechanisms.