BOOM is a synthesizable, parameterized, superscalar out-of-order RISC-V core designed to serve as the prototypical baseline processor for future micro-architectural studies of out-of-order processors. Our goal is to provide a readable, open-source implementation for use in education, research, and industry. BOOM is written in roughly 9,000 lines of the hardware construction language Chisel. We leveraged Berkeley's open-source Rocket-chip SoC generator, allowing us to quickly bring up an entire multi-core processor system (including caches and uncore) by replacing the in-order Rocket core with an out-of-order BOOM core. BOOM supports atomics, IEEE 754-2008 floating-point, and page-based virtual memory. We have demonstrated BOOM running Linux, SPEC CINT2006, and CoreMark.