This paper discusses the current development of research in touch sensing for robots, the major challenges, and the possible directions for future research. In the paper, I will briefly introduce the mechanism of humans' touch perception, which in years has provided lots of inspiration and guidance for roboticists to design tactile sensing frameworks. Apparently, the humans touch sensing capability is very powerful, mostly because it works as a system that integrates dynamic and static pressure sensing, kinesthetic perception, and the motion of limbs. Similarly, an intelligent touch sensing system for robots should also work as a \textit{system}, which contains multi-modal sensory input and integration with the robot's motion system. The questions are in both \textit{how} to build the system, and \textit{what} is the needed system.