What role do things play in a theory of the social? This question has been dedicated by the French philosopher and sociologist Bruno Latour to a good part of his highly productive research life. The essay “The Berlin Key” (1991) proposes a concept of action that is radically different from the relevant microsociological concepts: Using the example of the Berlin key, Latour shows how technical artifacts impose specific action programs on their users. In doing so, he unfolds based on precise descriptions the core thesis of the Actor-Network Theory (ANT): Social action does not originate from people. Instead, in the case of the Berlin key, a complex network of objects and people is ‘acting’, which extends far beyond time and space: an actor-network. Based on the selected essay, the central elements of the ANT are presented and contextualized. Even though the Actor-Network Theory is not a media theory in a strict sense, its potential for the analysis of digital infrastructures will be shown at the end.