A discussion of simulation languages, their characteristics, the reasons for using them, and their advantages and disadvantages relative to other kinds of programming languages. Simulation languages are shown to assist in the design of simulation models through their "world view," to expedite computer programming through their special purpose, high-level statements, and to encourage proper model analysis through their data collection, analysis, and reporting features. Ten particularly important simulation programming language features are identified: modeling a system's static state, modeling system dynamics, statistical sampling, data collection, analysis and display, monitoring and debugging, initialization and language usability. Examples of each of the four simulation languages, GPSS, SIMSCRIPT II, SIMULA, and CSL, are used to illustrate how these features are implemented in different languages. The future development of simulation programming languages is dependent on advances in the fields of computer languages, computer graphics, and time sharing. Some current research is noted, and outstanding research areas are identified.