This engaging case study describes a library instruction session held virtually for undergraduate students in an upper-level history course on US foreign relations. Working collaboratively, the special collections librarian and instruction librarian for history presented students with strategies for finding and evaluating digital primary sources for their research papers. Students were introduced to the role the curatorial process plays in the creation of digital collections. The instructors highlighted that such collections frequently contain only a portion of the materials in a full archival collection as well as the role of curatorial bias: digital collections often reflect the prejudices and interests of the person who selected the materials to be digitized. In some cases, this can mean less material in digital collections from underrepresented groups, hence the need to "mind the gap".