Delivering high-speed, pervasive wireless services to trillions of mobile devices requires a significant transformation to today's wireless cellular networks. Hyper-dense heterogeneous networks (HDHNs), enabled via a viral and large-scale deployment of small cell base stations and mobile devices, are seen as one of the cornerstones of this transformation. However, most existing network design and optimization techniques fall short in handling the scale, density, sustainability, and dynamics of such HDHNs.This project contributes to the foundations of HDHNs via innovations that include novel mobility state estimation techniques, optimized cell selection and handover methods, and a new game-theoretic framework for self-organizing resource management in energy-efficient HDHNs. The proposed approaches will be evaluated and enhanced via implementation on an experimental testbed using software radio and open source platforms. Boosting the performance of wireless systems will have societal impacts via enablement of novel mobile services requiring high-performance network connectivity. The project results will also support the analysis of dense networks and the development of future wireless standards and products. As a new Japan-US collaboration the project will build long-term relationships between US and Japanese researchers designing sustainable, energy-efficient and dense wireless systems. The project will create new educational and outreach activities to attract under-represented minorities to the field of sustainable HDHNs.