  This text is an introduction to an operational outlook on Bell inequalities,
which has been very fruitful in the past few years. It has lead to the
recognition that Bell tests have their own place in applied quantum
technologies, because they quantify non-classicality in a device-independent
way, that is, without any need to describe the degrees of freedom under study
and the measurements that are performed. At the more fundamental level, the
same device-independent outlook has allowed the falsification of several other
alternative models that could hope to reproduce the observed statistics while
keeping some classical features that quantum theory denies; and it has shed new
light on the long-standing quest for deriving quantum theory from physical
principles.
