What are the five programming languages defined by IEC 61131-3?

IEC 61131-3 defines five languages: (1) Ladder Diagram (LD) - graphical relay logic, (2) Function Block Diagram (FBD) - graphical data flow between blocks, (3) Structured Text (ST) - high-level textual language similar to Pascal, (4) Instruction List (IL) - low-level assembly-like language, (5) Sequential Function Chart (SFC) - graphical sequential/parallel process representation. Selection depends on application: LD for discrete logic, FBD for continuous control, ST for complex calculations, SFC for batch/sequence control. Modern PLCs support multiple languages in single project.