NASA's Discovery Program (as compared to New Frontiers, Explorers, or Flagship Programs) is a series of lower-cost, highly-focused American scientific space missions that are exploring the Solar System. It was founded in 1992 to implement then-NASA Administrator Daniel S. Goldin's vision of "faster, better, cheaper" planetary missions. Discovery missions differ from traditional NASA missions where targets and objectives are pre-specified. Instead, these cost-capped missions are proposed and led by a scientist called the Principal Investigator (PI). Proposing teams may include people from industry, small businesses, government laboratories, and universities. Proposals are selected through a competitive peer review process. All of the completed Discovery missions are accomplishing ground-breaking science and adding significantly to the body of knowledge about the Solar System.

NASA also accepts proposals for competitively selected Discovery Program Missions of Opportunity. This provides opportunities to participate in non-NASA missions by providing funding for a science instrument or hardware components of a science instrument or to re-purpose an existing NASA spacecraft. These opportunities are currently offered through NASA's Stand Alone Mission of Opportunity program.