When we consider the structural strength, first we calculate the structural responses to the external forces and then we judge whether the result is within the allowable limits which are determined according to the data from existing vessels. In the same manner, when we design a structure from a vibration aspect, we first calculate the structural response to the exciting forceExciting force and then we judge the result considering the allowable limits which are determined from human discomfort, structural damage, or the lifetime of the machinery. One important feature of hull structural vibration is that it is still difficult to calculate accurate natural frequencies and vibrational responses using numerical simulation. Therefore, it is essential to reply on empirical simple models established based on many measurement data on actual ships. Another important feature is that there are varieties of vibration prevention measures other than structural reinforcement. It is effective to reduce exciting forces by means of damper, balancer, phasing, highly skewed propeller, firing order of main engine cylinders, etc. Avoidance of resonance is also important. This chapter describes various exciting forces on ships, various mitigation measures of vibration and their effect based on many onboard measurement data, and anti-vibration design methods for superstructures, in-tank structures, and so on.