This series of articles by researchers from Kid Risk, Inc. offers critical insights to help national, regional, and global health leaders as they navigate the polio endgame. The series includes papers that explore the risks of a non-synchronous switch from oral poliovirus vaccine (OPV) containing serotypes 1, 2, and 3 (trivalent OPV or tOPV) to bivalent OPV (bOPV) containing serotypes 1 and 3, and the consequences of inadvertent use of tOPV after the global switch from tOPV-bOPV. One paper examines different options for responding to outbreaks that may occur during the endgame. Several papers in the series use a global model developed and applied in one paper to characterize the risks, costs, and benefits of different future poliovirus risk management options for 2013-2052 compared to the 2013 baseline of continued widespread use of OPV. One paper provides estimates of vaccine needs for different OPV formulations in the run up to coordinated OPV cessation of each serotype. The series includes a paper that shows the importance vaccine choice and of preferentially using tOPV for supplemental immunization activities in the run up to the switch. One paper reviews the available evidence and characterizes the potential for reintroductions of immunodeficiency-associated vaccine-derived polioviruses. Another paper explores alternative OPV cessation timing options that represented alternative paths to the current strategy.