Full ordination, upasampada, requires a candidate to have already spent time as a novice, samanera, under the ten precepts, and is then conferred by a quorum of already fully ordained bhikkhus, a minimum of five in some circumstances and ten in the standard case, meeting the requirements of a properly constituted ordination ceremony, sangha-kamma, whose procedural validity Vinaya law specifies in considerable detail, since an improperly conducted ordination is held to be invalid regardless of the candidate's own sincerity or qualification. This procedural requirement has given the bhikkhu sangha, the community of fully ordained monks, a strong emphasis on maintaining an unbroken, procedurally valid ordination lineage traceable, in principle, back through an unbroken chain of properly ordained monks to the Buddha's own original community.
Where a country's bhikkhu ordination lineage has been disrupted by war, persecution or simple decline in the number of remaining ordained monks capable of forming a valid ordaining quorum, restoring a valid lineage has sometimes required bringing monks from another country's still-intact lineage to perform the ordination, a practice that has occurred at various points across Buddhist history and remains a live consideration in some smaller or historically disrupted national Buddhist communities today.