It is pointed out that one must distinguish between causality as a general property of some physical theories expressing that the time development ofclosedsystems is determined if the initial state is suitably specified, and specific cause‐effect relations arising from the action of an outside agent on anopensystem. The connection between the space‐time structure of the special theory of relativity and its causality requirements is discussed briefly, and some common misunderstandings are clarified. The consequences of these requirements for classical relativistic theories of systems of interacting mass points are discussed; it is argued that they do not impose any restrictions on the description of closed systems, but only of open ones, since it is only the latter for which the concept of causal anomaly is physically meaningful. Thus no restrictions are imposed on the possible existence of particles moving faster than light (tachyons) within closed systems, but the possibility of purposeful production of and experimentation with tachyons must be excluded. Similarly, for closed systems, particles are not restricted to interactions describable by fields; indeed, at least to order c−2, any field‐theoretical interaction acting over intervals in or on the future light cone of the source (commonly mislabeled “causal”) is equivalent to an interaction (similarly mislabeled “noncausal”) acting over a space‐like interval.