Koeman, 44, left his post in charge of PSV Eindhoven earlier this week and has signed a two-and-a-half year deal with the Spanish outfit.
Former Holland and Barcelona defender Koeman replaces Quique Sanchez Flores, who was sacked after Sunday's 3-0 defeat at Sevilla.
"We wanted to sign an internationally recognised coach," said Valencia president Juan Soler.
"We are convinced we will be in very good hands. He knows what Valencia's objectives are, he knows the squad and he will bring us the success we want."
Source. BBC