sPHENIX is a state-of-the-art jet, upsilon and open heavy flavor experiment currently
under construction at the BNL Relativistic Heavy Ion Collider, RHIC. sPHENIX will take first physics data in 2023, performing measurements of hard-probe obervables of the Quark-Gluon Plasma complementary to those from the LHC experiments. In this article we describe the science mission, detector layout and key performance parameters of sPHENIX, and give illustrative examples of planned measurements in heavy-ion collisions.