Publisher Summary An average user appreciates a programming language looking at the easiness of programming, which depends mainly on its expressive power and its security. Generally, it is not necessary to understand even what the implementation of a programming language is. However, experienced programmers know quite well that without a deeper knowledge of some implementation aspects, the real software would never exist. This chapter discusses the kinds of programming languages; the module structure of a program; the blocks, procedures, and functions of a program; the cooperation of coroutines, coroutine sequencing, and the different passing modes of parameters. Some high level programming languages, like ALGOL 60, PL/1 and Pascal, allow procedures and functions as parameters, that is, they admit formal procedure construct. This important construct is easy in use; however, the precise semantics needs some deeper insight. One of the most important characteristics of classes is the possibility of defining abstract data types. An important feature that extends the power and the flexibility of classes is inheritance rule [CURR], [ING], [MEY], sometimes called prefixing [SIM]. Inheritance is a method for module extending by some new specifications and actions that are added to the previous ones. It can be said that such a module inherits all the properties of its parent module.