This article reviews the basic processes of fracture and fatigue and shows how these processes occur in materials. It presents an overview of the fatigue mechanisms and some related models for appropriate classes of materials, such as carbon and alloy steels, aluminum alloys, and titanium alloys. Microstructural factors that affect the fracture toughness of these materials, are discussed. The article describes fatigue crack propagation (FCP) mechanisms and related models. It also analyzes FCP behavior in these materials, with an emphasis on general microstructural factors.