Metadata is central for information organization in digital libraries. A growing number of digital libraries worldwide are now generating metadata to describe not only individual objects but entire digital collections as integral wholes. However, collection-level metadata has not yet been empirically evaluated. This paper reports results of the study that used an in-depth comparative content analysis to assess free-text collection-level subject metadata in three large-scale digital cultural heritage aggregations in the United States and Europe. As observed by this study, the emerging best practices include encoding a variety of information about a digital collection in free-text collection-level Description metadata element. This includes both subject-specific (topical, geographic and temporal coverage, and types/genres of objects in a digital collection) and non-subject-specific information: title, size, provenance, collection development, copyright, audience, navigation and functionality, language of items in a digital collection, frequency of additions, institutions that host a digital collection or contribute to it, funding sources, item creators, importance, uniqueness, and comprehensiveness of a digital collection.