Dictionarium Annamiticum Lusitanum et Latinum

The Dictionarium Annamiticum Lusitanum et Latinum (known in Vietnamese as Từ điển Việt-Bồ-La) is a trilingual Vietnamese-Portuguese-Latin dictionary written by the French Jesuit lexicographer Alexandre de Rhodes after 12 years in Vietnam. It was published by the Propaganda Fide in Rome in 1651, upon Rhodes' visit to Europe, along with his catechism Phép giảng tám ngày.

Before Rhodes's work, traditional Vietnamese dictionaries used to show the correspondences between Chinese characters and Vietnamese Chữ Nôm script. From the 17th century, Western missionaries started to devise a romanization system to represent the Vietnamese language in order to facilitate the propagation of the Christian faith, which culminated in the Dictionarium Annamiticum Lusitanum et Latinum of Alexandre de Rhodes. The dictionary has 8,000 Vietnamese entries with glosses in Portuguese and Latin.

Dictionarium Annamiticum Lusitanum et Latinum was itself inspired by two earlier lost works: a Vietnamese–Portuguese dictionary by Gaspar de Amaral and a Portuguese–Vietnamese dictionary by António Barbosa. The dictionary incorporates a summary on Vietnamese grammar (Brevis Declaratio) and codification of some contemporary pronunciations.

The dictionary established Quốc ngữ, the Vietnamese alphabet, which was refined by later missionaries and eventually became the predominant writing system for Vietnamese. Mgr Pigneau de Béhaine contributed to these improvements with his 1783 Annamite–Latin dictionary, the manuscript of which was remitted to Mgr Jean-Louis Taberd who published in 1838 his Vietnamese–Latin / Latin–Vietnamese dictionary.

Despite these efforts, Christian publications in Vietnam continued to use either Latin or the traditional Vietnamese Chữ Nôm rather than the simpler alphabetic Quốc ngữ for the next 200 years, and Quốc ngữ would only gain predominance with the French invasion of 1861 and the establishment of French Indochina.