Yoo (also often spelled Yu or Ryu), is a common Korean family name. As of 2000, there were about 1.04 million people by this name living in South Korea, making up roughly 2% of that country's population.
The surname "Yoo" can represent any of four hanja: 柳, 劉, 兪, and 庾. Of these the most common is 柳, with more than 600,000 holders in South Korea, whereas 兪 accounts for about 0.4 percent of the population at best.
Only the character 柳 is commonly pronounced Ryu or Ryoo (류). (see Munhwa Ryoo)
Notable clans include the Munhwa Ryoo and the Pungsan Ryoo.