Which of these is the most common Vietnamese family name?

Nguyen is a very common Vietnamese family name and usually refers to Nguyễn with diacritics and less commonly as Nguyên. Nguyễn is the most common Vietnamese family name. Outside Vietnam, the surname is commonly rendered without diacritics as Nguyen. Vietnamese pronunciations between south and north are similar, except for the distinct tone between the two dialects.

By some estimates forty percent of Vietnamese people bear this surname.

Nguyễn is derived from a Chinese surname. Nguyễn is the Vietnamese transliteration of the Chinese surname (阮), which is often transliterated as Ruan in Mandarin, Yuen in Cantonese, Gnieuh or Nyoe¹ /ɲɥø˩˧/ in Wu Chinese, or Nguang in Hokchew.

Many events in Vietnamese history have contributed to the name’s prominence. In 1232, after usurping the Lý Dynasty, Trần Thủ Độ forced the descendants of the Lý to change their surname to Nguyễn. When Hồ Quý Ly overturned the Trần Dynasty, he killed many of their descendants so when the Hồ Dynasty collapsed in 1407, many of his descendants changed their surname to Nguyễn in fear of retribution.

In 1592, on the collapse of the Mạc Dynasty, their descendants changed their surname to Nguyễn. When the Nguyễn Dynasty (the descendants of the Nguyễn Lords) took power in 1802, some of the descendants of the Trịnh Lords fearing retribution changed their surname to Nguyễn, while others fled north into China.