In this article I explore the interactional significance of grammar on turn-taking in Japanese in view of reported conversation analytic findings on turn-taking for Anglo-American English. In particular, I examine ways in which grammar may be implicated in the construction of turns at speaking and the projection of turn endings in Japanese talk-in-interaction. In a crude sense, the grammatical structures of Japanese and English can be regarded as polar opposites. This is reflected in dramatic differences in participant orientations to turn construction and projection in the respective languages. Specifically, in contrast to English grammar, which massively enables early projectability of the social action that might occupy a turn, the grammatical structure of Japanese permits incremental transformability of a turn in progress and overwhelmingly results in a later arrival of the point at which the emerging shape of a turn can be known. This delayed projectability in Japanese, however, is to a large extent compensated by a potentially greater degree of certitude with which participants can localize turn endings through devices that mark possible transition-relevance places.