This three-volume set LNCS 16431-16433 constitutes the refereed proceedings of the 12th International Conference on Behavioural and Social Computing, BESC 2025 held in Hong Kong SAR, China, during October 16–18, 2025. The 18 full papers and 5 short papers presented in this volumes were carefully reviewed and selected from 149 submissions. These papers focus on various aspects of social computing, applied psychology, behaviour pattern learning, text and sentimentanalysis, graph learning, AI in education, and AI for social good.