The aim of this paper is to characterize a type of causality relevant to study the closure of complex systems that we call formal causation. By this term we understand the existence of a new (not materially inherent) causal relation among constituents, generated through an autonomous process of closure. Once a certain level of organization is reached, material systems can generate internal constraints that, through recursive processes, construct their own identity. We study two different forms of closure: closure in dissipative systems and closure in template self-replication. Finally, these two forms merge and bring forth a new one: informational closure, We show how complex forms of organization are based on informational closure, which is an explicit, recorded type of formal causation allowing a functional articulation between individual organizations and larger, collective and historical (meta)organizations.