A number of approaches to providing authoritative researcher identifiers have emerged, but they tend to be limited by discipline, affiliation or publisher. This talk provides an overview of an OCLC Research task group's analysis of a complex ecosystem of systems and institutions that provide, aggregate and use researcher and name authorities: researcher identifier systems. The presentation reflects on the state of the practice and on the remaining challenges to the integration of researcher identifiers into the systems and practices of libraries, universities, funders, and publishers.