The word accent system of Tokyo Japanese might look quite complex with a number of accent patterns and rules. However, recent research has shown that it is not as complex as has been assumed if one incorporates the notion of markedness into the analysis: nouns have only two productive accent patterns, the antepenultimate and the unaccented pattern, and different accent rules can be generalized if one focuses on these two productive accent patterns. The word accent system raises some new interesting issues. One of them concerns the fact that a majority of nouns are ‘unaccented,’ that is, they are pronounced with a rather flat pitch pattern, apparently violating the principle of obligatoriness. A careful analysis of noun accentuation reveals that this strange accent pattern occurs in some linguistically predictable structures. In morphologically simplex nouns, it typically tends to emerge in four-mora nouns ending in a sequence of light syllables. In compound nouns, on the other hand, it emerges due to multiple factors, such as compound-final deaccenting morphemes, deaccenting pseudo-morphemes, and some types of prosodic configurations. Japanese pitch accent exhibits an interesting aspect in its interactions with other phonological and linguistic structures. For example, the accent of compound nouns is closely related with rendaku, or sequential voicing; the choice between the accented and unaccented patterns in certain types of compound nouns correlates with the presence or absence of the sequential voicing. Moreover, whether the compound accent rule applies to a certain compound depends on its internal morphosyntactic configuration as well as its meaning; alternatively, the compound accent rule is blocked in certain types of morphosyntactic and semantic structures. Finally, careful analysis of word accent sheds new light on the syllable structure of the language, notably on two interrelated questions about diphthong-hood and super-heavy syllables. It provides crucial insight into ‘diphthongs,’ or the question of which vowel sequence constitutes a diphthong, against a vowel sequence across a syllable boundary. It also presents new evidence against trimoraic syllables in the language.