We have investigated the initial stages of Cu(001) oxidation using in situ ultra-high vacuum (UHV) transmission electron microscopy (TEM) from 10(-5) torr O-2 to atmospheric pressures and temperature range from room temperature to 600 degreesC. The advantages of in situ TEM experiments include visualization of oxidation processes in real time and information on buried interfaces. We have previously demonstrated that the initial stages of copper oxidation in dry oxygen is a surface-limited process. To investigate the effect of oxidizing environments, we have examined the oxidation of Cu(001) with water vapor and noted the surprising reduction of copper oxides in contrast to thermochemical data. We are also modelling the nucleation to coalescence of the oxide scale using the Johnson-Mehi-Avrami-Kolmogorov (JMAK) equation and noted a qualitative agreement.