Abstract: Design-for-debug (DFD) has become an important feature of modern VLSI. On the one hand, traditional pre-silicon verification methods are not sufficient to enssure the quality of modern complex VLSI designs, thus employing DFD to facilitate post-silicon verification has attracted wide interests from both academia and industry; on the other hand, debugging parallel program is a world-wide difficult problem, which cries out for DFD hardware supports. In this paper, we analyze the existing structures of DFD comprehensively and introduce different fields of DFD for debugging hardware and software. These fields contain various kinds of DFD infrastructures, such as the DFD infrastructure for the pipe line of processor, the system-on-chips (SOC) and the networks on multi-cores processor. We also introduce the recent researches on how to design the DFD infrastructures with certain processor architecture and how to use the DFD infrastructures to solve the debug problems in these different fields. The topologic of the whole infrastructure, the hardware design of components, the methods of analyzing signals, the compressing and storing signals, the using of DFD infrastructure in debugging parallel program and post-silicon debugging are all introduced. Furthermore, some possible future directions of DFD research are given based on the state-of-the-art literatures and industrial requirements.