This talk focuses on Romaji, the romanization of Japanese. While Japanese is commonly described as using three writing systems—Hiragana, Katakana, and Kanji—Romaji functions as a “fourth writing system” in a number of domains, including public signage, computer input, and auxiliary tools for learners of Japanese. The talk first overviews the history of Romaji, highlighting the early documentation of Japanese by European missionaries since the sixteenth century, as well as later attempts to institutionalize Romaji by abolishing Kana and Kanji in the Meiji era. It then examines how different systems of romanization reflect aspects of Japanese phonology, shedding light on questions often raised by learners regarding the apparent inconsistencies of Romaji. Finally, the talk discusses recent developments in national policies on Romaji in the context of the increasing internationalization of Japanese society, arguing that Romaji—often treated as peripheral—reveals important aspects of both Japanese linguistics and language policy.