This chapter will be concerned with a number of distinctive morphosyntactic and semantic properties of adpositions and their projections, i.e. adpositional phrases (PPs). Section 32.1 begins with a general characterization of the category of adpositions. Sections 32.2 and 32.3 then discuss two possible ways of classifying adpositions. The first classification is syntactic, in that it is based on the relative position of adpositions with respect to their complement (if any). This leads to the following four syntactic classes: prepositions, postpositions, circumpositions, and intransitive adpositions (including the so-called verbal particles). The second classification is based on the meaning of the adpositions, which leads to the following three semantic classes: spatial, temporal, and non-spatial/temporal adpositions. Section 32.4 concludes with a discussion of a number of borderline cases, i.e. elements that resemble adpositions in various ways, but for which it is not immediately obvious that they should really be considered adpositions.