The two-volume set LNAI 8265 and LNAI 8266 constitutes the proceedings of the 12th Mexican International Conference on Artificial Intelligence, MICAI 2013, held in Mexico City in November 2013. A total of 85 papers presented in these proceedings were carefully reviewed and selected from 284 submissions. The first volume addresses advances in artificial intelligence and its applications and is structured into five sections: logic and reasoning; knowledge-based systems and multi-agent systems; natural language processing; machine translation; and bioinformatics and medical applications. The second volume focuses on advances in soft computing and its applications and is organized into eight sections: evolutionary and nature-inspired metaheuristic algorithms; neural networks and hybrid intelligent systems; fuzzy systems; machine learning; and pattern recognition.