The electroplating of copper by the damascene process is the predominantly used technique for on-chip wiring in the fabrication of ultra-large scale integrated microchips. In this process, void-free superconformal filling of trenches is achieved by multicomponent electrolytes, containing chloride and organic additives in addition to the Cu ions. In this paper we review studies of the atomic-scale Cu interface structure and homoepitaxial Cu electrodeposition behavior in acidic (pH 1-3) Cl-containing electrolyte by in-situ surface X-ray diffraction. This technique provides detailed insight on the 3D atomic arrangement at the electrode surface and fast time-resolved data on the kinetic growth mode. On Cu(111) a complex potential-dependent adlayer structure is found, involving transitions between a chemisorbed oxygen species to a hexagonal close-packed incommensurate chloride adlayer. In contrast, on Cu(001) a simple disorder-order transition to a c(2 x 2) Cl adlayer is found. Parallel to the latter, a crossover from step-flow to layer-by-layer and finally 3D growth occurs during Cu(001) electrodeposition, indicating a decreasing Cu surface mobility toward more positive potentials. The presence of the organic additive polyethylene glycol (PEG) stabilizes the partial c(2 x 2) Cl adlayer on the Cu(001) surface and leads to an inhibition of Cu deposition with a tendency to rougher growth. (C) The Author(s) 2018. Published by ECS.