The bonding mode of the copper ion in various formulations of a well‐known electroless copper bath consisting of copper sulfate, sodium hydroxide, potassium sodium tartrate, and formaldehyde has been determined by electron paramagnetic resonance spectroscopy. Other ligands related to tartrate in structure, but with fewer potential bonding sites, were also studied. It was discovered that 2,3‐butane diol, α‐hydroxy butyric acid, malic acid, glycolic acid, and mandelic acid could be substituted for tartrate in an electroless copper bath, but that succinic acid, β‐hydroxy butyric acid, and salicylic acid could not. The plating rate of copper‐tartrate solutions as a function of pH was studied, and it was found that the maximum plating rate occurs at about pH 12.8. The structure of the copper complex is pH dependent and is one factor affecting the deposition rate.