Much attention has been paid to the semantic aspects of Japanese numeral classifiers, and in particular, the semantic constraints which govern which classifiers co-occur with which nouns (Yo, 1993; Bond and Paik, 2000). Here, we focus on a more neglected aspect of this linguistic phenomenon, namely the syntax of numeral classifiers: How they combine with number names to create numeral classifier phrases, how they modify head nouns, and how they can occur as stand-alone NPs. We find that there is both broad similarity and differences in detail across different types of numeral classifiers in their syntactic and semantic behavior. We present semantic representations for two types of numeral classifiers, and describe how they can be constructed compositionally in an implemented broad-coverage HPSG (Pollard and Sag, 1994) for Japanese. The grammar of Japanese in question is JACY, originally developed as part of the Verbmobil project (Siegel, 2000) to handle spoken Japanese, and then extended to handle informal written Japanese (email text; (Siegel and Bender, 2002)) and newspaper text. Recently, it has been adapted to be consistent with the LinGO Grammar Matrix (Bender et al., 2002).