This paper examines the frequently discussed quantifierdou ‘all’ in Mandarin Chinese. I argue, following traditional grammarians as well as Lee (1986), thatdou ‘all’ is an adverb of quantification. I show that a floating quantifier analysis ofdou ‘all’ along the lines of Chiu (1990, 1993) falls short of accounting for the dual status ofdou, as a quantifier and a binder. As a quantifier,dou quantifies over regular NPs (plural). As a binder,dou provides quantificational force forwh-polarity items, which do not have inherent quantificational force. I argue that the locality restrictions associated withdou varies depending on the element it is associated with. With regular NPs, the locality is reflected by LF adjunction ofdou. Withwh-polarity items, the locality is restricted by licensing of polarity items as well as its ability as a binder.