LuaRadio is a lightweight, embeddable flow graph signal processing framework for software-defined radio. It provides a suite of source, sink, and processing blocks, with a simple API for defining flow graphs, running flow graphs, creating blocks, and creating data types. LuaRadio is built on LuaJIT, has a small binary footprint of under 750 KB (including LuaJIT), has no external hard dependencies, and is MIT licensed. LuaRadio can be used to rapidly prototype software radios, modulation/demodulation utilities, and signal processing experiments. It can also be embedded into existing radio applications to serve as a user scriptable engine for processing samples.