In this exploratory study, we map the use of free and open source software (FOSS) in the United States energy sector, especially as it relates to cyber security. Through two surveys and a set of semi-structured interviews—targeting both developers and policy makers—we identified key stakeholders, organizations, and FOSS projects, be they rooted in industry, academia, or public policy space that influence software and security practices in the energy sector. We explored FOSS tools, common attitudes and concerns, and challenges with regard to FOSS adoption. More than a dozen themes were identified from interviews and surveys. Of these, drivers for adoption and risks associated with FOSS were the most prevalent. More specifically, the misperceptions of FOSS, the new security challenges presented by the smart grid, and the extensive influence of vendors in this space play the largest roles in FOSS adoption in the energy sector.