Results are presented for a study on the influence of molecular and polymeric carboxylate-containing additives on the nucleation of CaCO3 in solutions similar in ion composition and pH to those used in wood pulping operations. Investigated additives included aminocarboxylic acids, ethylenediaminetetraacetic acid and diethylenetriaminepentaacetic acid, and two carboxylic acid containing polymers, a poly(acrylic acid) and a poly(maleic acid). Temperatures necessary to induce rapid nucleation in supersaturated solutions increased with the addition of these species, and the data were well characterized by a form of classical nucleation theory that relates nucleation temperatures to supersaturation. Extracted fitting parameters indicate distinctly different influences for the aminocarboxylic acids and carboxylic acid containing polymers. Parameters found for the aminocarboxylates were the same as those found when no additive was present. In contrast, fitting parameters changed significantly with increasing concentrations of the carboxylate-containing polyelectrolytes. The results are consistent with solution-phase and interfacial interactions for the aminocarboxylates and weak acid polyelectrolytes, respectively. Deconvolution of these effects from nucleation data measured in the presence of combinations of ethylenediaminetetraacetic acid and a poly(acrylic acid) was also demonstrated. Results indicate that classical nucleation theory can be applied to identify the primary mechanism by which additives influence nucleation processes and provide a means for making direct comparisons of performance.