Donation after circulatory death (DCD) donors differ from donation after brain death (DBD) donors in that they experience a period of obligatory donor warm ischemia time (DWIT) prior to initiation of cold perfusion of organs. While most authors agree that prolonged DWIT results in hepatic ischemic injury, debate exists on the length DWIT or hemodynamic parameters following withdrawal of life support that determine whether a liver graft can be used with reasonable safety. As such, the concept of a functional warm ischemic time (fDWIT) arose from the notion that individual events during DCD procurement, such as variations in hemodynamics, mandatory wait period, time from incision to cannulation of the aorta and cross-clamp, all of which are included in total DWIT, may have different impact on the outcome of the liver graft. In addition, the recent increased utilization of both in situ and ex situ perfusion has undoubtedly changed the thresholds of DWIT that were developed with static cold storage (SCS). The present chapter reviews the various definitions relevant to warm ischemia time in liver transplantation using DCD donors in an attempt to clarify the existing ambiguity. The chapter also provides a comprehensive view of the literature by describing studies that have investigated various parameters of warm ischemia time and their associations with outcomes following liver transplant using DCD donors, such as graft failure and ischemic cholangiopathy (IC). Finally, the chapter reviews updated information on prolonged fDWIT and outcomes with in situ and ex situ perfusion.