Originally introduced by French biologist Pierre-Paul Grassé in 1959 to describe a coordination mechanism used by insects, the term “stigmergy” describes the principle that the work of a single agent-whether natural, animal or human-always leaves a trace that stimulates an action. Today, the notion of stigmergy has various applications in a growing spectrum of fields, including robotics, online communities and human society. In Collective Keywords, the Parasite 2.0 collective of architects – who work acting within a hybrid of architecture, art and social sciences – collects a series of examples of collective activities, starting precisely from the idea that any action or mark left in the environment can initiate a series of subsequent actions; be it children’s games or micro-architectures, exhibition projects or pop-up architectures designed as a tool for political participation. Collective Keywords is part of the Visual Essay Series, a collection of books for those seeking new visual cues for looking at reality.