In this book, the authors present current research in the study of the mechanisms, behaviour and analysis of fatigue crack growths. Topics discussed in this compilation include the unified fatigue crack growth rate model; practical tools for statistical fatigue design; probablistic algorithms performance evaluation and application in multi-fractured structures; three dimensional effects in the fracture mechanics of bi-dimensional specimens; fatigue crack propagation mechanism in porous open pore metal foams; lifetime predictions for short fatigue crack's initiation-propagation by basic mechanical properties; variable amplitude fatigue crack growth in selected aluminium alloys; fatigue threshold R-curves for analysis of short fatigue cracks; and multiaxial fatigue life prediction for lateral notched round bars made of high strength steel.