In this paper, the authors report on a study aimed at harmonising two nursing terminologies, the Clinical Care Classification (CCC) and the International Classification for Nursing Practice (ICNP®). As the electronic health record evolves and the need for interoperability extends beyond local and national borders, a degree of standardisation across healthcare terminologies become essential. Harmonising across terminologies results in a) increased consensus relating to domain content and b) improvements in the terminologies involved. Findings from this study suggest that there is much overlap of content in nursing terminologies. The continued harmonisation between nursing terminologies and other healthcare terminologies are recommended to achieve international interoperability.