Digital libraries evolved in response to the need to manage the vast quantities of electronic information that we produce, collect, and consume. Architects of such systems have adopted a variety of design approaches, which are summarized and illustrated in this chapter. We also introduce the following three chapters, and provide suitable background. From a historical perspective, we note that early systems were designed independently to afford services to specific communities. Since then, systems that store and mediate access to information have become commonplace and are scattered all over the Internet. Consequently, information retrieval also has to contend with distributed/networked systems in a transparent and scalable fashion. In this context, digital library architects have adopted various interoperability standards and practices to provide users with seamless access to highly distributed information sources. This chapter looks at current research and emerging best practices adopted in designing digital libraries, whether individual or distributed.