Thermal response of electrodeposited copper has been characterized by monitoring changes in microstructure, tensile strength, elongation, and microhardness following 30 minute isothermal anneal at temperatures between 23 and 450°C. By judicious control of additives to the electrolyte, considerable enhancements of strength, hardness, and anneal resistance are obtained. When recrystallization is shifted to higher temperatures, annealing proceeds by recovery-like processes; prior to the onset of recrystallization, significant strength loss may occur by recovery. Recrystallization initiates near the substrate side of the deposit and progresses along an uneven front across the deposit thickness. The microhardness and tensile response monitors indicate several unusual anneal-related microstructural processes: (i) precipitation (of microvoids) hardening, (ii) dissolution and reprecipitation, (iii) stepped progress of recovery and recrystallization, and (iv) embrittlement (loss of elongation) at low anneal temperatures and prior to the onset of recrystallization.