What is the oldest existing organisation?

Answer 1

The Roman Catholic Church is the oldest continuously operating entity with an identifiable structure. Verifiably, the first pope was Linus (after Peter, anyway), who took office in AD 64 or 67, depending upon the source. The office of the papacy as the head of the church has not been left vacant since that time. I mention the Roman Catholic Church because there is dispute concerning the role of the leadership in Rome during the early church, particularly among the Orthodox. However, the Roman bishop, or pope, was unquestionably the patriarch of the western church. Thus, disputes over Peter's papacy aside, the central structure of the Roman church has existed for about 1950 years at this point. Orthodox churches cannot lay claim to this age, if only because their episcopates have been overrun at times, particularly due to Muslim conquest. More specifically, the more ancient sees that were on par with Rome (Alexandria, Antioch, Jerusalem, and Constantinople), either did not exist as early as Rome (Constantinople), or disappeared before the turn of the millennium (all of the rest).

No secular institution can come even close to such longevity (governmental or otherwise). The U.S. presently has the oldest continuously operating government at about 225 years, though some claim that Iceland has had a continuously operating parliament for about 1100 years. As for other religions, Hinduism, the world's oldest known religion, has no institutional structure, as such. Judaism, another of the world's oldest religions, has had its institutional structure destroyed at several points in time, notably during the Babylonian exile, and again after the Roman destruction of the temple in 67 AD. Modern Judaism is divided (as it has been for over 2000 years), and does not share a common institutional structure with its historical predecessors.

Answer 2

The Boys' Brigade founded in 1883 by Sir William Smith in Glasgow. This Christian organisation exists in many countries on all continents. Started 25 years before the Scout Movement.