The increasing popularity of systems on a chip, where processors are just a small fraction of the design, calls into question why one of the most important interfaces is proprietary. We argue that: * There is no good technical reason not to have free, open instruction sets just as we have free, open networking standards and free, open operating systems. * The most likely first targets for a free, open instruction set are systems on a chip for the Internet of Things, which have low cost and power demands, and for Warehouse Scale Computers, which could benefit from viable alternatives to the 80x86 instruction set * The best architectural style for a free, open instruction set is RISC. * Given the time it takes to design an instruction set, it makes more sense to adopt an existing RISC free, open instruction set than to design a new one from scratch. * Among the existing RISC free, open instruction sets, RISC-V is the best and safest choice.