The nucleation properties and thermal stability of the copper on MgO(100) have been investigated with variable temperature atomic force microscopy. Using non-contact imaging techniques, the nucleation and diffusion of submonolayer coverages of copper on MgO(100) have been visualized over the temperature range of 300-750 K. For deposition at 300 K, islands one to two layers in thickness form across the terraces of the MgO surface. Upon annealing, the average diameter of the copper islands increases slowly between 300 and 550 K. At higher temperatures, a dramatic increase in island diameter and height occurs. Time dependent images of the Cu/MgO system at temperatures above 550 K reveal a complex evolution of the island structures involving growth, decay, coalescence, and diffusion of the islands.