The document calls for papers for a special issue of the Springer journal Mobile Network & Applications (MONET) on networking in 5G mobile communication systems. It discusses the challenges of meeting 1000 times increase in wireless traffic by 2020 compared to 2010. 5G networks will require fundamental rethinking from the system architecture down to the physical layer to provide data-intensive services in dense areas with quality of service guarantees and energy efficiency. Small cells will be prominent in 5G for high capacity and energy efficiency. The special issue solicits original research and tutorial articles on networking aspects and technologies for 5G systems like small cell deployment, dense networks, and massive MIMO to improve throughput, energy efficiency, and quality of experience.