It has long been observed that the superlative construction, exemplified by John climbed the highest mountain, has two readings. On the absolute reading, the heights of the relevant mountains in a relevant context are compared; on the comparative reading, relevant climbers’ achievements of mountain climbing are compared (Szabolcsi, Comparative superlatives, MIT Working Papers in Linguistics, 1986). Two theories have been proposed regarding this ambiguity. One theory holds that it results from movement of the superlative morpheme -est (movement theory) (Heim, Association with focus, Doctoral Dissertation, 1985, Notes on superlatives, 1999; Szabolcsi 1986).The other theory holds that the ambiguity is derived by assignment of different values to the context variable C, keeping a single LF structure where -est stays in situ (in-situ theory) (Farkas and Kiss, Nat Lang Linguist Theory 18:417–455, 2000; Sharvit and Stateva, Linguist Philos 25:453–504, 2002). As is pointed out by Heim (1999), a choice between these theories is hard to make based solely on English. Through an investigation of Japanese superlative constructions, this paper argues that, in Japanese at least, a movement theory is required.