Occlusal vertical dimension is important in all aspects of prosthodontics. Unfortunately, there is no scientific method of determining the correct occlusal vertical dimension. The amount of interocclusal rest space (IRS) is a rough guide since muscle tone, which determines the space, is variable. IRS varies greatly from one patient to the next. It will automatically be correct when the occlusal vertical dimension is correct. IRS should not be interfered with regardless of its size. Many techniques have been used for determining occlusal vertical dimension in dentulous and edentulous patients. Regardless of the technique, the occlusal vertical dimension must be determined carefully by the dentist for a successful prosthesis.