In order to fully assess the critiques articulated and positions developed in this book, it is useful to review the different ways in which language has been conceived of in reference not to the abstraction Language but to any of the multitude of languages practiced around the world today. It has been described by linguists alternatively as a ‘system of units and rules’ used by its practitioners to communicate, as a ‘representation system’ reflecting a culture-specific world view, and as a ‘communication practice’. All of these are at variance with the folk conception that means the ‘way a particular population speaks’ (alas, typically excluding signed languages!). The latter way is also consistent with the various words used for a language. They vary cross-linguistically and sometimes intra-linguistically, for instance, ‘tongue’, ‘voice’, ‘speech’, idiome/idioma (in French/Spanish), and ‘language’ < Latin lingua ‘tongue’. For the purposes of this book, I submit we conceive of it, from an evolutionary perspective, as technology for explicit and high-fidelity communication. We can thus compare language shift, which produces language endangerment and loss (LEL), with other technology shifts, so that we can assess the processes as outcomes of people’s adaptative responses to changing ecologies or ecosystems.