WiOpt 2014, the 12th International Symposium on Modeling and Optimization in Mobile, Ad Hoc, and Wireless Networks is an international forum aiming to facilitate the flow of expertise between researchers and practicioners working on modeling and optimization of wireless network design and operations. As such, WiOpt 2014 solicits previously unpublished high-quality contributions that propose original performance evaluation methodologies (or different perspectives on older ones), new results on the performance limits of wireless networks (simulation-based or theoretic) and novel algorithms and optimization methods with which to attain them. WiOpt 2014 covers all types of wireless networks: cellular (both wide and local area networks), metropolitan, ad hoc (both dense and sparse), sensor, delay-tolerant, mesh, content-driven, vehicular, or any convex combination of the above. Contributions to the symposium should provide a significant improvement over the existing state-of-the-art for the design, analysis, and operational envelope of wireless networks, either by offering new insights on theoretical aspects (information-theoretic capacity, etc.), or by proposing novel practical optimization methods and tools.