This paper presents the results of a Delphi study conducted over a two-month period in 2011. The purpose of the study was to identify reference sources that should be covered in basic reference courses taught in LIS programs in the United States. The Delphi method was selected for its appropriateness in soliciting expert opinions and assessing the relative salience of issues and is considered appropriate for investigating questions that can benefit from subjective input from a group of highly qualified experts. The study included one pre-test round with six experts. After refining the instruments, four rounds were conducted using a panel of twelve experts. The panel of experts was composed of librarians in different types of libraries who have regular experience in providing reference services and reference instruction in LIS. Results show consensus and a high level of agreement on 54% of the resources presented to the list. In addition to the numeric data, the study includes qualitative comments from the experts that explain and justify their choices. A bibliography is included.