Artificial Intelligence is present in almost every aspect of our lives, and is highly discussed in human-machine ethics. Nevertheless, the clarification of the conceptual framework is still in the making, particularly when we are dealing with or co-acting with (semi-)autonomous systems. In such situations, questions about the distribution of responsibility arise. In recent years, a debate about so-called “responsibility gaps” has arisen. The chapter aims to clarify the concept of co-action by exploring its roots and relating it to issues surrounding responsibility.