This book mainly focus on ball bearing fault diagnosis and effect of unbalancing on bearing vibrations. The bearing failure is the major cause in the machine failure. Failure of rolling element bearing occurs due to manufacturing errors, improper assembly, bearing faults, misalignment, unbalance and because of too harsh an environment. However, even if a bearing is perfectly made, assembled, it will eventually fail due to fatigue of the bearing material. Unbalance is a common feature of all rotational elements. Generally, each unbalance of mass in rotary motion is the source of rotational forces and moments of inertial forces which, being transferred through the bearings to the body of the machine, results vibrations in the whole system.So condition monitoring of these bearing is important. The study investigated the variation response characteristics of ball bearing for balanced and unbalanced rotor-bearing system. The study also investigated the dynamic characteristics of ball bearing for change in parameters such as eccentricity, unbalancing mass, size of defect, position of the defect on outer race of bearing and shaft speed experimentally and using an MATLAB programming.