Definition: Social mobility is a person’s movement over time from one class to another. Social mobility can be up or down and can be either intergenerational (occurring between generations, such as when a child rises above the class of his or her parents) or intragenerational (occurring within a generation, such as when an individual changes class because of business success). Societies differ in the extent to which social mobility is permitted. Some societies are based on closed class systems in which movement from one class to another is nearly impossible. In a caste system, for example, mobility is strictly limited by the circumstances of one’s birth. At the other extreme are open class systems in which class system placement is based on individual achievement rather than ascription.