Slovenian is one of the very few modern Indo-European languages with a productive three-way number opposition across all major categories. Additionally, the expression of number is part of a complex fusional inflectional system; on nouns alone, the three-way number opposition interacts with the expression of three grammatical genders, six cases, and inflection class differences. The morphological patterns that emerge display a large amount of number syncretism, numberconditioned syncretism, as well as interesting patterns of number-conditioned suppletion and allomorphy. In the realm of syntax, quantified noun phrases display an extremely complex pattern of number and case marking interactions, which in turn have consequences for verbal agreement, including mismatches in number agreement between auxiliary verbs and participles and complex patterns of agreement with conjoined noun phrases. Finally, the three-way number system has interesting consequences for the lexical distribution and semantics of number on nouns, in particular cases of seemingly optional dual number.