An experimental approach was developed for imaging the nucleation and growth of individual oxide-supported nanoparticles and their subsequent in situ chemical and thermal treatments by scanning tunneling microscopy (STM). The potential of the method is demonstrated for Au nanoparticles supported on a reduced TiO(2) substrate where a cluster-by-cluster comparison is made of the morphological evolution and stability of nanoparticles during their nucleation and thermal annealing. Using this methodology the details of the nucleation and growth kinetics can be directly observed.