Petri nets were invented in 1962. They predate Unix, the internet, and object-oriented programming. For most of their history, they lived in academic papers — a formalism known to theorists but invisible to working programmers.

This book argues they deserve wider use. Not because they're elegant (they are) but because they solve practical problems. A Petri net is a state machine that handles concurrency. It's a workflow engine with formal guarantees. It's a simulation model that converts to differential equations. It's a specification that can be verified, compiled to code, and proven in zero knowledge.