A comprehensive treatment on the topic of PLC (Programmable Logic Controller) hardware and software. It concentrates primarily on the Allen-Bradley and Siemens PLC platforms, but includes examples from many other brands. The first section covers PLCs from a generic perspective, discussing features that are common to all platforms along with their differences. This section also has a history of computers and computing devices along with the evolution of the PLC. The book explains many of the mathematical and data concepts that are necessary for programming PLCs, and describes the five IEC61131 PLC languages with examples of each. It explains the ladder logic programming instructions common to PLC platforms and includes 12 exercises, complete with answers in the back of the book. The second section covers advanced PLC topics including planning and organizing PLC code. It discusses common subroutine types including System, Input and Output routines, Auto Sequences, Faults and Alarms.