Copper electrorefineries operating with high nickel concentrations have reported that the presence of Ni2+ has led to increased nodulation as well as decreasing current efficiency and increased frequency of dendrite growth. High nickel concentrations may also promote passivation and affect the forming of the slime layer and thus indirectly negatively influence the cathode quality and contamination. This chapter summarizes the recent experimental observations that researchers at Aalto University have made regarding the behavior of nickel in copper electrorefining. Nickel contamination has been mainly attributed to contamination caused by anode slime; however, the electrolyte inclusions have also been found to possibly occur with the potential for major nickel contamination. In recent studies, nickel-containing particles have not been directly linked to nodulation nor does nickel have a significant impact on the cathode roughness, but nickel has been found to influence the formation of slime layer and thus indirectly causing cathode contamination.