Pe̍h-ōe-jī, meaning 'vernacular writing,' is a system for transcribing variants of Hokkien Southern Min, particularly Taiwanese and Amoy Hokkien. Developed by Western missionaries in Southeast Asia during the 19th century and refined in Xiamen and Tainan, it utilizes a modified Latin alphabet with diacritics to represent the spoken language. Initially successful in Fujian, it became most widespread in Taiwan, where it was used for a significant amount of printed material, including Taiwan's first newspaper. The script faced periods of suppression but continues to be used by various groups in Taiwan, with full computer support achieved in the early 21st century.

The system's development was pedagogical, aimed at educating Christian converts. Early work by Walter Henry Medhurst in the 1820s introduced a dictionary and consistent tone markings, influenced by linguistic studies. Later refinements by missionaries like Elihu Doty and John Van Nest Talmage established a pre-modern version of the orthography. The pronunciation standard was based on the speech of Xiamen and later adapted for Taiwan. While some missionaries viewed Pe̍h-ōe-jī as a stepping stone to Chinese characters, others advocated for it as a standalone writing system. It laid the groundwork for new literature in Taiwan and was officially recognized as a standard spelling system for Southern Min in 2006.

Pe̍h-ōe-jī, also known as Church Romanization, originated in the 19th century through the efforts of Western missionaries working with Chinese diaspora communities in Southeast Asia. Walter Henry Medhurst produced an early dictionary in 1820, incorporating consistent tone markings vital for understanding Southern Min, influenced by contemporary linguistic studies. This foundational work, though differing from the modern system, guided later compilers. Elihu Doty's 1853 manual represented a significant step towards the pre-modern POJ, with its tone mark system remaining intact in contemporary usage. Missionaries in Xiamen and later Taiwan adapted the script to the local speech, establishing a de facto standard based on the Xiamen dialect. The system's development was closely tied to the propagation of Christianity and pedagogical aims.

Pe̍h-ōe-jī achieved considerable readership, with hundreds of thousands of users at its peak, particularly in Taiwan. It was instrumental in producing a large volume of religious and secular texts, including Taiwan's inaugural newspaper, the Taiwan Church News. Despite periods of suppression under Japanese rule and subsequent martial law in Taiwan, and a decline in mainland China, the script has persisted. It continues to be utilized by Taiwanese Christians, learners of Southern Min, and enthusiasts. The system's influence extended to the creation of new literature in Taiwan, preserving Southern Min vocabulary since the late 19th century. In 2006, Taiwan's Ministry of Education announced the Taiwanese Romanization System (Tâi-lô), a successor based on Pe̍h-ōe-jī, though debates surrounding writing systems for Taiwanese persist.

The name Pe̍h-ōe-jī translates to 'vernacular writing' and specifically refers to the Southern Min romanization system developed by Presbyterian missionaries. Alternative terms like 'Church Romanization' emerged due to its strong association with Christian communities, though this name is contested as the script is also used in secular contexts. Some object to 'Pe̍h-ōe-jī' because it can encompass multiple systems and registers, while others dislike 'romanization' for potentially diminishing its status as a standalone orthography. Variations of the system have been developed for other Chinese dialects, such as Hakka and Teochew. The ongoing evolution and official recognition of related systems highlight the dynamic nature of vernacular writing in the region.

“Respecting these tones of the Chinese language, some difference of opinion has been obtained, and while some have considered them of first importance, others have paid them little or no intention. The author inclines decidedly to the former opinion; having found, from uniform experience, that without strict attention to tones, it is impossible for a person to make himself understood in Hok-këèn.”