Now that the global eradication of wild poliovirus is almost within sight, planning for the post-certification era is becoming a priority issue. It is agreed that a stockpile of appropriate polio vaccines will need to be established, and a surveillance and response capacity will need to be maintained, in order to protect the world against any possible future outbreaks attributable either to the persistence of wild poliovirus or vaccine-derived polioviruses (VDPVs) or to the unintentional or intentional release of poliovirus from a laboratory or vaccine store. Although it has been suggested that the stockpile should consist of monovalent oral poliovirus vaccine (mOPV), many questions remain concerning its nature, financing, management, and use--in particular, because of uncertainties over future national vaccination policies, and over the availability of different vaccines, after the certification of wild poliovirus eradication. There are further uncertainties concerning the possible role and efficacy of inactivated poliovirus vaccine (IPV) used either routinely or in outbreak control in low-hygiene settings, the potential for rapid geographical spread of polioviruses should an outbreak occur after certification, and the risks inherent in introducing additional oral polio vaccine (OPV) viruses into populations in which the vaccine coverage and prevalence of immunity have declined, and which may thus favour the spread of VDPVs. Given these important gaps in knowledge, no country should discontinue polio vaccination until a coordinated policy for the post-certification era has been developed and the recommended measures have been put in place.