The undoubted success of Fortran as the predominant programming language in the field of scientific and numerical computing is due, in part, to the steady evolution of the language. Following the publication of the first two standards of 1966 and 1978, the technical committee responsible for their development, X3J3, has worked in conjunction with an ISO committee to develop a new standard suitable for use in the 1990s. This new standard, called Fortran 90, contains the new features required for large scale computing on modern supercomputers, but still retains all of the familiar features that have made the language so popular. This book is a description of this new language, providing a comprehensive guide to all its features. its authors are both members of X3J3 and have many years of experience in the use of Fortran. The book is intended for new and existing Fortran users, and for all those involved in any aspect of scientific and numerical computing.