This monograph explores the grammar of modifier PPs in Japanese, concentrating on their word order. The study argues that (i) modifier PPs are hierarchically arranged and (ii) there is an interesting fine-grained correlation between different PP types and Modal/Aspect functors which indicates that Temporal and Locative appear relatively freely with respect to a certain range of the Modal/Aspect functors in the middle field, whereas the rest of the PP types are more constrained in this respect. Unlike cartographic approaches to PPs (Schweikert 2005, Cinque 2006), the book adopts the working hypothesis that the fine-grained hierarchies can be derived in a constrained manner along the lines of Svenonius and Ramchand (2014) and proposes that the properties of the PPs characterized by (i) and (ii) can be captured in a sortal domain analysis. The book appeals to a linguistic audience interested in modifier syntax as well as in Japanese.