This course discusses the principles of fracture as a vital criteria in design of probably defected solids and structures, for which the presence of cracks or notches may cause severe reduction in the strength of the structure, while the usual strength-based design codes do not completely consider such effects. The most important topics presented during the course include, but are not limited to: Importance of Fracture Mechanics, Linear Elastic Fracture Mechanics (LEFM), Stress Intensity Factor (SIF), Elasto-Plastic Fracture Mechanics (EPFM), Brittle and Cohesive crack propagation, Crack Tip Opening Displacement (CTOD), Numerical Fracture Mechanics in 2D and 3D Problems, eXtended Finite Element Method (XFEM), Rock and Concrete Fracture, smeared crack models, Fatigue Crack Growth.