This volume constitutes the refereed proceedings of the 18th International Conference on Software Process Improvement and Capability Determination, SPICE 2018, held in Tessaloniki, Greece, in October 2018. The 26 full papers presented were carefully reviewed and selected from 40 submissions. The papers are organized in the following topical sections: SPI systematic literature reviews, SPI and assessment, SPI methods and reference models, SPI education and management issues, SPI knowledge and change processes, SPI compliance and configuration, SPI and agile, industry short papers.