This book focuses on surface layers fracture of cyclical contacting bodies (machine parts). Calculation models and calculating procedures of stress-strain states of cyclically contacting solids with cracks, are included. Recommendations for the optimization of operating parameters of joints (contact stresses magnitude, friction/lubrication conditions, materials crack resistance etc) for elements of rolling pairs (wheel–rail systems, backup roll – working roll of rolling mills etc.) and some fretting pairs are formulated.