This book constitutes the refereed proceedings of the 12th International Conference on Practical Applications of Agents and Multi-Agent Systems, PAAMS 2014, held in Salamanca, Spain, in June 2014. The 12 revised full papers and 14 short papers were carefully reviewed and selected from 52 submissions and are presented together with 19 demonstrations. The papers report on the application and validation of agent-based models, methods, and technologies in a number of key application areas, including: agent-oriented software engineering, conversations, motion coordination and unmanned aerial vehicles, web and service systems, robotics exploration, smart cities and infrastructures, and social systems.