Abraham Maslow developed a motivational theory, called the "Need-Hierarchy" theory, which postulates that people constantly strive to meet needs that have not yet been satisfied. According to this theory, needs are arranged in a sequential hierarchy, from lower-order to higher-order needs. Once a lower-order need is satisfied, that need no longer motivates behavior and people seek to satisfy the next set of needs in the hierarchy. The following are the five needs levels, listed in order of priority from lowest to highest: