The CCIS book constitutes selected papers of the 12th International Conference on Computational Science and Computational Intelligence, CSCI 2025, which took place in Las Vegas, NV, USA, during December 3&5, 2025. The 38 full papers and 4 poster papers included in this book were carefully reviewed and selected from a total of 389 submissions to the Research Track on Artificial Intelligence, CSCI-RTAI. They were organized in topical sections as follows: Learning Strategies - Transfer Learning and Reinforcement Learning; Artificial Intelligence - Applications of Graphs and Networks; Artificial Intelligence - Natural Language Processing & Large Language Models; Artificial Intelligence - Prediction and Forecasting Methods; Artificial Intelligence - Algorithms and Applications; and Poster Papers.