Book excerpt: Whether it is to look to the past in search of their origins, analyze their present activity, particularly digital, or to think about the effects of their actions on the future, 21st century humans regularly question their traces. Collective questions and technical progress offer new resources which, in turn, raise the problems of traces. In order to reveal the difficulties posed by the unanalyzed trace, this book proposes a journey through different contexts. Along the way, intellectuals (including Bateson, Barthes, Bourdieu, Derrida, Goffman, Peirce, Ricoeur, Varela, Thompson, Watsuji and Watzlawick) and trace professionals (such as police officers or computer scientists) shed light on the background to this veritable odyssey. This didactic book presents a contemporary exploration of the fundamental nature of the trace via the new French paradigm of the Ichnos-Anthropos (Homme-trace) and its corollary, the corps-trace.