Like many new ideas, object oriented programming (OOP) does not yet have a universally accepted definition. Even the terminology of OOP can vary greatly from one system or language to another. This paper introduces OOP to the newcomer in a language-independent manner. The underlying theory of OOP is presented to give the reader the basics necessary to understand the nuances of the various OOP languages that are available. Several OOP languages are briefly considered, as are object-oriented database management systems, object-based programming, and object-oriented design. Various problem areas are explore in detail. This paper should also be of considerable help in making the transition from one OOP language to another.