The Valdivia Expedition, or Deutsche Tiefsee-Expedition (German Deep Sea Expedition), was a scientific expedition organised and funded by the German Empire under Kaiser Wilhelm II and was named after the ship which was bought and outfitted for the expedition, the SS Valdivia. It was led by the marine biologist Carl Chun and the expedition ran from 1898-1899 with the purpose of exploring the depths of the oceans below 500 fathoms, which had not been explored by the earlier Challenger Expedition.
In the mid-19th century most scientists adhered to the Abyssus theory which posited that it was not possible for life to exist below 300 fathoms depth. Carl Chun, a famed teuthologist, held a deep conviction that there must be life, in abundance, which existed in the unknown abyssal regions of the oceans and he proposed that the German Empire organise its own expedition which was to be nationally funded with the approval of the Kaiser.