This repository contains the formal specification of the M17 digital radio protocol, an open-source amateur radio standard. It is a single LaTeX document (M17_spec.tex) that defines the physical layer (4FSK modulation, synchronization, randomizer), data link layer (frame types, forward error correction, stream/packet/BERT modes), and application layer (voice, data, encryption, digital signatures). The specification is exhaustive, including mathematical definitions, encoding algorithms, and reference C code snippets. The repository also includes a CI workflow that automatically generates a PDF from the LaTeX source and deploys it to GitHub Pages. While not a software application itself, this spec serves as the authoritative reference for implementing M17-compatible radios and software. The document is actively maintained with frequent revisions and contributions from multiple authors.