This book constitutes the refereed proceedings of the 18th International Symposium on Search-Based Software Engineering, SSBSE 2026, held in Montreal, QC, Canada, during July 2026.

The 5 full papers, with 10 short papers included, in these proceedings were carefully reviewed and selected from 23 submissions. The symposium featured four tracks: the Research Track, the SBSE Challenge Track, the Hot-off-the-Press (HOP) Track, and the Replications, Negative Results, and New Ideas
& Emerging Results (RENE/NIER) Track.