Aimed at improving a programmers ability for altering code to fit changing requirements and for detecting and correcting errors, this book argues for a new way of thinking about maintaining software. It proposes the use of a set of human factors principles that govern the programmer-software-event world interactions and form the core of the maintenance process. The book is thus highly valuable for systems analysts and programmers, managers seeking to reduce costs, researchers looking at solutions to the maintenance problem, and students learning to write clear unambiguous programs.