Noun-Verb compounding and Verb-Verb compounding in Japanese are shown to have typologically notable properties. The applicability of Japanese N-V compounding, unlike Noun Incorporation in polysynthetic languages, is controlled by the tensedness or finiteness of the verb constituents: it has little productivity with tensed or finite verb constituents, whereas it gains increased productivity if the verb constituents take non-finite (adnominal and gerundive) forms. The uniqueness of Japanese V-V compounding, on the other hand, is argued to be ascribed to a special group of "lexical aspectual compound verbs," where the first member determines the argument relations of a whole compound and the second member supplies a variety of Aktionsart meanings to the event denoted by the first member. This type of lexical compound verb, a new discovery, contrasts sharply with the familiar group of "lexical thematic compound verbs" in which the second member determines the argument relations of a whole compound, with the first member semantically modifying the second member in some way or other.