Keeping and breeding animals which are threatened with extinction in their natural habitat, should be one of the most important tasks of zoological gardens today. Efforts should be focussed on finding the zootechnical solution of problems which will arise inevitably, especially if rare species, or those that have the reputation of being difficult to keep or to breed, are concerned. The Orang-Utan ( Pongo pygmaeus (Hoppius)) has been kept in Zoos for more than a century. As a matter of fact this species was on exhibition regularly in the Zoos of the Netherlands during the nineteenth century. Orang-Utans were, a hundred years ago, much more common in the Zoological Gardens of Amsterdam and Rotterdam than Chimpanzees. Longevity records however were very poor indeed. Hundreds and hundreds of these apes must have been imported on Dutch ships to keep up a regular stock. This is not surprising, because the least knowledge of the basic needs of these apes was lacking. Unsuitable food, lack of medicine and the wrong opinion that tropical animals should be kept in overheated quarters, caused the death of innumerable animals. The direct cause of death was either intestinal trouble or Tuberculosis. Under these circumstances breeding could not be expected. The first female Orang-Utan which came to a Zoo with its baby, the famous Buschi in Dresden Zoo, caused quite a sensation. But even in recent times the breeding of apes proved to be difficult. With better zoo-technical knowledge, Chimpanzees can be bred regularly. Orang-Utan and Gorilla however maintained the reputation of being difficult breeders. The first Zoo that started breeding Orangs regularly was Philadelphia. Afterwards several other Zoos, among which the Royal Rotterdam Zoo, succeeded in building up a breeding group. The Rotterdam Zoo was the first in breeding a second generation.