An electron microscopic investigation has revealed that the electroless deposition of copper occurs by repeated three‐dimensional nucleation at catalytic sites on a substrate. The nature of the catalytic sites formed by immersion in the standard stannous and palladium chloride solutions was observed and found to influence the structure of the subsequently deposited metal. Initially, copper nuclei about 25Aå in diameter form aggregates an order of magnitude larger. As the autocatalytic reduction reaction continues the aggregates increase in size until they become energetically unstable; then recrystallization occurs. The resulting continuous copper films exhibit a heterogeneous microstructure with grain size variations of more than an order of magnitude and also numerous twin faults.