  The intriguing phenomenon of many-body localization (MBL) has attracted
significant interest recently, but a complete characterization is still
lacking. In this work, we introduce the total correlations, a concept from
quantum information theory capturing multi-partite correlations, to the study
of this phenomenon. We demonstrate that the total correlations of the diagonal
ensemble provides a meaningful diagnostic tool to pin-down, probe, and better
understand the MBL transition and ergodicity breaking in quantum systems. In
particular, we show that the total correlations has sub-linear dependence on
the system size in delocalized, ergodic phases, whereas we find that it scales
extensively in the localized phase developing a pronounced peak at the
transition. We exemplify the power of our approach by means of an exact
diagonalization study of a Heisenberg spin chain in a disordered field.
