The fourth edition of this text and reference remains focused on the current ANSI 83 standard and reflects the imminent Ada 9X standard in three ways: highlights all features of Ada that will be affected by the Ada 9X standard, and describes their design rationale in detail; summarizes important changes, including the increased support for object-oriented programming, the introduction of hierarchical library structure and the inclusion of protected objects; and provides details syntax changes in appendices for easy access.