Abstract: RISC-V has experienced rapid growth and widespread adoption since its inception in 2010. It stands out as an instruction set not only because of its relative youth, but also because of its open nature. As a modern instruction set, RISC-V’s architects have drawn lessons from decades of prior instruction set designs. This article introduces several key design decisions of RISC-V, discusses how RISC-V differs from earlier instruction sets, and illustrates how RISC-V has learned from the successes and failures of its forerunners.