The evolution of Web-based learning has fostered the search for methods and technologies that enable a degree of reuse of learning contents and learning activity designs. Such attempt is intended to facilitate both the reuse of quality resources and the development of automated resource-search tools, and it may eventually reduce the cost of devising learning activities. The concept of learning object is at the center of a new instructional design paradigm for Web-based learning. This new paradigm emphasizes reuse as a quality characteristic of learning contents and activities. For example, the often-cited definition of learning object by Polsani (2003) explicitly includes reuse in his definition: “an independent and self-standing unit of learning content that is predisposed to reuse in multiple instructional contexts.” In one of the most referenced articles on the field, Wiley (2001) also mentions the term reuse in his learning object definition: “any digital resource that can be reused to support learning.” Nevertheless, the concept of learning object reusability as a key quality factor for content design is difficult to characterize and measure, since it encompasses not only the evaluation of the contents themselves (Vargo, Nesbit, Belfer, & Archambault, 2003), but also a balance between their usability in specific contexts and the range of educational contexts it explicitly targets (Sicilia & Garcia, 2003). In practical terms, a learning object is a piece of Web content of arbitrary type and structure described by a metadata record. This metadata record provides information about the object and its prospective educational usages. Learning object metadata, thus, is the key to reuse.