Nucleation rates for the formation of ice from water have been calculated from observations of the frequency with which liquid droplets solidify. The stochastic nature of these solidifications has been considered and statistical methods employed for weighting observations and predicting experimental errors. The dependence of the solidification frequency on droplet volume and temperature has also been considered and methods were found for incorporating these dependencies into the rate calculations. The influence of the droplets' environment on the nucleation process was found in most cases to be negligible. The nucleation rates obtained from isothermal and continuous cooling experiments were in good agreement with each other, and their temperature dependence was in accord with the functional relationship predicted by theory. The rate's temperature dependence indicated a transition from a heterogeneous to a homogeneous nucleation mechanism; this finding was supported by the rate's dependence on droplet radius, which indicated a surface catalysis for the heterogeneous data. The average experimental kinetic constant was found to be greater than the theoretical value by a factor of 10 15 • 6 • This discrepancy could be explained by invoking a temperature dependent ice-water interfacial free energy.