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. Examples of PLC code are included from several platforms. An overview of training hardware is included along with a lab exercise to write a complete hardware-based program for a training model. A full program solution is included in the back of the book. The third section covers the Allen-Bradley PLC brand, including the SLC/Micrologix RSLogix500 platform and the CompactLogix/ControlLogix RSLogix5000 platform. It also covers the Siemens PLC brand, including the S7-300/S7-400 Step 7 platform, and the Siemens S7-1200/S7-1500 TIA Portal platform. Hardware model descriptions, instruction sets, and examples of creating and programming the four types of PLC are included, with information on platform specific languages including Siemens STL.