This book chapter uncovers the fundamentals of weld repair. It presents different definitions and explanations of welding as a process and the defects associated with pre-weld and post-weld activities. Welding repair as a secondary operation and categories of repair welding are discussed alongside processes and repair procedures. This chapter also highlights heat treatment activities and unveils from researches the benefits of weld repair in terms of improved mechanical and chemical properties for advanced industrial engineering production.