Personality science has always been and is still ready for new theorizing on traits. Accordingly, this article presents the recently proposed traits as hierarchical systems (THS) model, where personality traits are not only the emergent properties of the three‐level hierarchy of the personality system, but are also hierarchical per se. As hierarchical systems, they are organized into three levels: mechanisms and processes, structures, and behavioral markers. In this approach, trait denotes the underlying, recurrent mechanisms that pattern its structure and account for the stability/variability of individual characteristics. Here, traits might be described as processes with a slow rate of change that can be substituted for structure. The main function of personality traits, within the personality system, is stimulation processing. Three dominant functions of stimulation processing in traits are proposed: reactive, regulative, and self‐regulative. Some important questions regarding the concept of trait remain, such as those concerning trait stability, determinacy, measurement, their relation to overt behaviors, personality type or state, and differentiation between temperament traits and other‐than‐temperament personality traits. All of these topics are discussed in this article, as well as the compatible and distinctive features of this approach in relation to selected modern trait theories.