The Vietnamese alphabet, called Chữ Quốc Ngữ (script of the national language), usually shortened to Quốc Ngữ (national language), is the current writing system for the Vietnamese language. It is based on the Latin alphabet (more specifically the Portuguese version of it^[1]) with some digraphs and the addition of nine accent marks or diacritics — four of them to create additional sounds, and the other five to indicate the tone of each word. The many diacritics, often two on the same letter, make written Vietnamese easily recognizable.

via: http://en.wikipedia.org/wiki/Vietnamese_alphabet

Download PDF – Chu Cai & Dau Thanh

http://www.vscso.org/lachong/Classes/2006/Level%201B/Bai%201%20-%20Chu%20Cai%20&%20Dau%20Thanh.pdf