After the 1988 World Health Assembly resolution to eradicate poliomyelitis, the Global Laboratory Network for Poliomyelitis Eradication (the laboratory network) was established by the World Health Organization (WHO). The laboratory network is one component of the international surveillance system for detecting polio through notification of cases of acute flaccid paralysis (AFP). As progress is made in eradicating polio worldwide, the laboratory network provides critical virologic evidence about where poliovirus is circulating as a guide to supplementary vaccination activities aimed at interrupting transmission. This report summarizes the laboratory data for documenting the decline in wild poliovirus transmission and the occurrence of vaccine-derived polioviruses and highlights the expanding role of the laboratory network in global polio eradication.