India is the most populous of the four remaining countries (including Afghanistan, Nigeria, and Pakistan) where transmission of wild poliovirus (WPV) has never been interrupted. The last cases of WPV type 2 worldwide were reported in October 1999 in India. However, transmission of WPV type 1 (WPV1) and WPV type 3 (WPV3) persists in India in the northern states of Uttar Pradesh and Bihar. Transmission of indigenous WPV in all of India's other states was successfully interrupted in 2002, and all WPV cases reported since then in the country have resulted from WPV circulating in Uttar Pradesh and Bihar. This report updates previous reports and summarizes India's progress toward polio eradication since January 2007, as of May 29, 2009. In 2005, the government of India introduced the use of monovalent oral polio vaccine type 1 (mOPV1), which has higher efficacy against WPV1 than does trivalent oral polio vaccine (tOPV), in supplementary immunization activities. After a multistate WPV1 outbreak in 2006, preferential use of mOPV1 was accelerated and WPV1 cases decreased from 83 in 2007 to 18 during January-May 2009. A resurgence of WPV3 cases in Uttar Pradesh in 2007 led to an outbreak in Bihar. SIAs using monovalent type 3 OPV (mOPV3) were expanded in 2007, and the number of WPV3 cases declined from 794 in 2007 to 41 during January-May 2009. Simultaneously interrupting transmission in high-risk areas of western Uttar Pradesh and Bihar is the key to successful interruption of all WPV transmission in India.