The seasonal dependence and life cycle of the interannual seesaw between the surface Aleutian and Icelandic lows (AL and IL, respectively) are investigated. It is found that the correlation between the AL and IL intensities is significantly negative only from February to mid-March. It is also found that the seesaw exhibits an equivalent barotropic structure. The AL and IL anomalies constituting the seesaw do not develop simultaneously over the North Pacific and the North Atlantic, respectively. Rather, the seesaw appears to form in association with the propagation of wave activity accumulated in early winter over the North Pacific into the North Atlantic in midwinter in the form of a Rossby wavetrain across North America. The anomalies over the North Atlantic become matured and are maintained through the feedback forcing from high-frequency transients along the Atlantic stormtrack. The AL-IL seesaw is robust in a sense that it appears even after removing either the Arctic Oscillation or El /Southern Oscillation signal.