A person, once baptized, cannot be baptized again. There was an ancient practice in some areas of rebaptizing those who had returned to the church from [[heresy]], but that practice has been universally rejected.

The various jurisdictions of the Orthodox Church generally accept baptism performed by other denominations as valid, subject to certain conditions. It is only possible to be baptized once, thus people with valid baptisms from other denominations may not be baptized again on [[conversion]]. Instead, for these converts the sacrament of chrismation is performed. However, in some cases it can be difficult to decide whether the original baptism was valid, so if there is any doubt, a conditional baptism is employed, in which the officiant says something of the form of "if you are not yet baptized, I baptize you..." The need for conditional baptisms is motivated not only by factual uncertainties regarding the original baptism, but also by the uncertainty of some of the baptismal theology regarding the precise conditions for the validity of baptism. (The Church holds that one cannot be certain that opinions which are offered by pious theologians, but on which the Church has not made an authoritative pronouncement, are correct, and even authoritative pronouncements can have multiple interpretations which the Church has neither definitively endorsed or rejected.)