This paper describes a number of argument selectors for grammatical relations in Kubeo, an Eastern Tukanoan language spoken in the Vaupes River area in Northwestern Amazonia. The main selectors discussed in this paper are: verbal agreement, case marking, constituent ordering, causative, applicative, non-finite clauses, passive, noun incorporation and anaphoric constructions. The overwhelming grammatical pattern selects S, A, and A ditr for similar treatment in contrast to the remaining argument types; some constructions suggest a distinction between two types of S arguments, which we analyze as S a versus S p . The language presents the phenomenon of differential object marking, as well as analytical challenges related to non-canonical passivization and the way that animacy, referentiality and argument hierarchies correlate in the organization of grammatical relations.