This paper is a brief introduction to this special issue of the International Journal of American Linguistics on argument-encoding systems of the little known languages of Bolivian Amazonia, a region extremely rich linguistically. After providing some information on the sociolinguistic settings and the history of linguistic research in this area, the paper focuses on the domain of argument-encoding systems in those languages. It shows how very diverse types of systems are found in languages spoken in very close proximity, including hierarchical/inverse cross-referencing systems, ergative systems and split-intransitive systems. The paper also points to a number of typologically and theoretically interesting phenomena found in these languages such as fluid transitivity, double object ditransitive constructions, and rare valency-changing derivations such as multiple applicatives and sociative causatives. Finally, the paper presents the contents of this special issue.