There has been an explosion of interest in, and books on, object-oriented programming (OOP). Why have yet another book on the subject? In the past a basic education was intended to result in mastery of the three r's: reading, 'riting, and 'rithmetic. Today a sound education in engineering programming leads to producing code that satisfies the four r's: readability, reusability, reliability, and real efficiency. Although some object-oriented programming languages have some of these abilities, Fortran 90/95 offers all of them for engineering applications. Thus, this book is intended to take a different tack by using the Fortran 90/95 language as its main OOP tool. With more than 100 pure and hybrid object-oriented languages available, one must be selective in deciding which ones merit the effort of learning to utilize them. There are millions of Fortran programmers, and so it is logical to present the hybrid object-oriented features of Fortran 90/95 to them to update and expand their programming skills. This work provides an introduction to Fortran 90 as well as to OOP concepts. Even with the current release (Fortran 95) we will demonstrate that Fortran offers essentially all of the tools recommended for OOP techniques. It is expected that Fortran 200X will offer additional object-oriented capabilities such as declaring “extensible” (or virtual) functions. Thus, it is expected that the tools learned here will be of value far into the future.