Millennial climate oscillations of the glacial interval are interrupted by extreme events, the so-called Heinrich events of the North Atlantic. Their near-global footprint is a testament to coherent interactions among Earth's atmosphere, oceans, and cryosphere on millennial timescales. Heinrich detritus appears to have been derived from the region around Hudson Strait. It was deposited over approximately 500 +/- 250 years. Several mechanisms have been proposed for the origin of the layers: binge-purge cycle of the Laurentide ice sheet, jokulhlaup activity from a Hudson Bay lake, and an ice shelf buildup/collapse fed by Hudson Strait. To determine the origin of the Heinrich events, I recommend (1) further studies of the timing and duration of the events, (2) further sedimentology study near the Hudson Strait, and (3) greater spatial and temporal resolution studies of the layers as well as their precursory intervals. Studies of previous glacial intervals may also provide important constraints.