Maintenance and repair of machinery in a petrochemical process plant was defined in a preceding volume as simply "defending machinery equipment against deterioration." Machinery maintenance can often be quite costly in a petrochemical plant operation. Prior to the publication of the first two volumes of this series, very few studies were available describing quantitative or objective methods for arriving at the optimization of the four strategies. Though our readers should not expect detailed contributions to those subjects in this volume, we did opt to include an overview section describing the maintenance philosophy practiced in a large multi-plant corporation which makes effective use of centralized staff and computerized planning and tracking methods. The term repair are often reserved for maintenance actions that improve the conditions of an item, but may or may not establish "good as new" condition. In fact, repair is strictly reserved for maintenance of an item that has reached a defined failed state or defect limit.