Abstract: The research field of digital libraries must be viewed as a union of subfields from a variety of domains combined with new research issues in order to realize its full potential. A clear exposition of the research issues involved has notyet been given. Most approaches to building digital library systems have thus far been limited to addressing specific digital library problems as variations of problems from other fields. This paper presents a taxonomy of digital library elements. Consideration of the elements in this taxonomy helps suggest a variety of issues. Example elements and some issues they suggest are used to populate the taxonomy. The paper continues by presenting a general digital library system architecture. Issues suggested by the taxonomy are shown to have implications at many levels of digital library system architectures for both design and implementation. This is illustrated by considering the implications of one issue (personalizing presentations) at several architectural levels and in the context of a set of current technologies.