Wireless mesh networks enable numerous embedded applications to be independent of the issues of wiring costs and physical constraints. At the same time, the unique nature of the wireless mesh networks requires many fundamental challenges to be addressed. Among them, robustness and the scalability are most important issues that need to be addressed. In typical wireless mesh network systems, these two factors generally go against each other due to the self-adjusting and non-hierarchical nature of the networks. For example, as the number of nodes increases, the robustness of network becomes harder to guarantee. On the other hand, to make the network more robust, smaller sized networks are preferred. When the issue of network responsiveness is added on top of these two issues, the equation becomes even more complicated. In this presentation, the reason that scalability is a difficult issue in wireless mesh networks is addressed, and the relationship among robustness, scalability and responsiveness will be discussed. In addition, several novel factors and approaches for improving the scalability of wireless sensor networks are presented.