To improve the solvent extraction purification of copper in leach solutions, studies were made to determine the equilibria relationships and kinetics of the extraction of copper from an aqueous phase into organic phases containing hydroxyoxime extractants. Equilibrium measurements from shakeout experiments indicate the extraction involves a complete displacement of ammonia ligands from the coordination sphere of the cupric ion by the extractant molecules, the extraction coefficient being sensitive to ammonia concentration, and ph. The results were explained by considering the stability of the various cupric ammine complexes. The kinetics of extraction, from single-drop experiments, appear to be controlled by mass transfer in the dispersed phase which is suggested by an activation energy of 2.6 Kcal/mole. Based on first principles, the mass transfer process is explained to be due to molecular diffusion for small drop sizes while convective transport contributes significantly to the reaction rate for larger drop sizes. The rate of copper extraction from ammonia solutions is considerably faster than from acidic solution.