'Ceremonial-year shrine transfer'. Usually refers to the ceremonial transfer of the kami of Ise Jingu to the adjacent shrine, rebuilt every twenty years. The latest (61 st) sengu ceremony at Ise took place in 1993, though the complex preparatory and concluding rites take several years on either side of the transfer date. Other major shrines are supposed to be rebuilt at intervals but the cost is prohibitively high. One theory is that the ritual derives from an original custom of rebuilding the shrine every year, with renewal rites on each occasion to re-empower the deity and that the rebuilding took place less often when more permanent shrine structures came into fashion. Another theory is that the rebuilding takes place each (human) generation. The rite of renewal probably owes its origin equally to Chinese (Taoist) sources.
A Popular Dictionary of Shinto. Brian Bocking.