All the different languages have the function of providing the easy programming, program modification and allowing the user the choice of a most appropriate language for a particular application. In this way the ease of use and maximum functionality is achieved without placing any constraints on the possible application of a PLC system. The standardisation of the PLC languages and the programming styles has meant that the common set of languages, the subject of this report, is supported by all the manufacturers of the PLC systems. Together with all the other advantages the PLC systems have over the relay logic systems, they have assumed a dominant position once held by the relay logic controllers in the field of process and automated manufacturing control.