This chapter introduces OpenDLib, a digital library service system developed at ISTI-CNR for easing the creation and management of digital libraries. It discusses the motivations underlying the development of such a system and describes it by presenting (i) the characteristics of the huge kind of content it is capable of managing, (ii) the set of functions it natively provides its digital libraries with, (iii) the powerful and flexibility of its component-oriented architectural paradigm as a key feature for addressing different application scenarios, and (iv) the technologies the system development relies on. The authors hope that understanding the OpenDLib foundational principles will not only inform stakeholders and decision makers of the features implemented by this existing system, but also assist researchers and application developers in the understanding of the issues, and their possible solutions, that arises when building digital library systems aimed at serving such a broad class of application scenarios.