During 1952-1954, some of the first papers were published on the attenuation of wild poliovirus for vaccine purposes. These efforts soon came to fruition , and large-scale field trials were held in many countries under a variety of conditions. Routine use of live oral poliovirus vaccines ( OPV ) was begun in many countries during the spring of 1960, and vaccines made from the Sabin strains were licensed in the United States in 1961-1962. In the early years of immunization with OPV , vaccines were usually monovalent, but a trivalent vaccine is now used. Throughout the world the introduction and continued proper use of OPV has been followed by a striking decrease in the number of paralytic cases. This dramatic and persistent outcome has stimulated recent discussions on the possible eradication of the disease. This paper reviews the criteria for the selection of vaccine strains that now make up the OPV , thermal stabilization of OPV , safety precautions that are followed in the manufacture of OPV , genetic stability of OPV strains following replication in vaccines and their contacts, and potential incorporation into OPV of totally attenuated polioviruses that can no longer revert to neurovirulence because the regions of the viral genome associated with neurovirulence are deleted or altered.