This talk will discuss some relevant networking issues for 5G mmWave cellular systems. First, we will give an extensive discussion on the potential benefits and technical challenges of spectrum sharing in ammWave context. We will show that from this points of view this scenario is much more promising than traditional cellular systems in sub-6 GHz bands. We will also discuss the role of coordination between different operators for the purpose of managing the inter- and intra-system interference, which is shown to be the ultimate limiting factor in spectrum sharing. Second, we will discuss how directionality makes it more difficult to implement and operate network management functionalities, with specific reference to Initial Access and Cell Search, where the energy/latency/detection tradeoff is of particular interest. Finally, we will briefly describe our full-stack 5G mmWave cellular simulator, which includes the whole protocol suite as well as detailed mmWave channel models, and present some examples of system-level results it can provide.