This chapter covers the design, development, and manufacture of the SLS Core Stage. As background, the Apollo Saturn V first stage and the Space Transportation System are briefly described as technological precursors for the eventual Space Launch System. The contract award for the Core Stage goes to the Boeing Corporation which will be responsible for the design, development, and manufacture at the Michoud Assembly Facility. The first flight Core Stage is test-fired at Stennis Space Center in 2020. This Core Stage is approved for flight and delivered to Kennedy Space Center in 2021 for the Artemis I mission.