System Dynamics (SD) is considered a causal modeling approach. Causality is a key and peculiar characteristic of SD: SD models are supposed to contain and represent only causal relationships. However, SD researchers are often not explicit about the notion of causality employed in their work, and there not seem to be a commonly adopted and clear definition of causality in the field. This paper investigates and compares the notions of causality emerging from the work of three major SD authors. The objective is to assess the extent to which a convergence towards a common definition of causality in the field exists, and whether the notion of causality used by the various authors is influenced by the particular field of application. The analysis conduced indicates that the notions of causalities used are similar, and that existing differences could be explained by different fields of application and different backgrounds of the authors.