Abstract:Aggregators are one of the important content providers for libraries. Libraries have been working with publishers and aggregators for many years; however, the issues related to aggregators are not well documented. Aggregators have been helping libraries to facilitate their services to users but they have some disadvantages for libraries such as the lack of library influence in selecting individual titles; the lack of control over the contents of aggregator packages and the confusion of library users when accessing different packages. This paper defines different types of aggregators and discusses their importance for libraries in the digital era. The paper provides a useful overview to researchers in any field, enabling them quickly to achieve a clear picture of aggregators in the electronic environment.