Modbus is one of the oldest industrial network protocols in existence, yet still the #3 in popularity. As of July 2018, a new version appeared on the market. Surprisingly, no one ever wrote a detailed book about Modbus. In this publication the author, who has some 30 years of experience with Modbus, gives a good introduction to the protocol in all its versions, with industrial networking background explained as well. Also, the author has added a lot of practical information about how to handle the different implementations of the protocol, the way of wiring a network, and troubleshooting tips