There have been recent claims that the early-2000s hiatus, when the rate of global warming slowed compared to the previous two decades, was an artifact of problematic sea surface temperature (SST) data, lack of Arctic data, or both.  The recent literature is reviewed to determine the current state-of-knowledge of the early-2000s hiatus or “slowdown” of global warming.  The evidence reveals that the hiatus is real and is mostly the product of internal variability, with small contributions from a series of moderate-sized volcanic eruptions.  Thus, the hiatus is a characteristic of ubiquitous internally generated decadal timescale variability in observations and models, with decade and longer periods of reduced globally averaged surface air temperature trends compared to the long-term multi-decadal forced trend.  Hiatus periods are typically associated with the negative phase of the Interdecadal Pacific Oscillation (IPO).  Processes associated with the IPO, particularly with regards to ocean mixing, provide the physical process evidence base to understand what produces hiatus periods such as the one we have been experiencing since about the year 2000.