Fracture toughness is the ability of a material to withstand fracture in the presence of cracks. This article focuses on the use of fracture toughness as a parameter for engineering and design purposes. Both linear elastic and elastic-plastic fracture mechanics concepts are reviewed as they relate to fracture toughness and design process. The article explores the use of plane strain fracture toughness, crack-tip opening displacement, and the J-integral as the criteria for the design and safe operation of structures and mechanical components. It discusses the variables affecting fracture toughness, including yield strength, loading rate, temperature, and material thickness. A summary of different fatigue and fracture mechanics design philosophies and their relationship with fracture toughness is provided. The article concludes with information on the examples of fracture toughness in design.