  In the theory of quantum communications, a deeper structure has been recently
unveiled, showing that the capacity does not completely characterize the
channel ability to transmit information due to phenomena -- namely,
superadditivity, superactivation and causal activation -- with no counterpart
in the classical world. Although how deep goes this structure is yet to be
fully uncovered, it is crucial for the communication engineering community to
own the implications of these phenomena for understanding and deriving the
fundamental limits of communications. Hence, the aim of this treatise is to
shed light on these phenomena by providing the reader with an easy access and
guide towards the relevant literature and the prominent results from a
communication engineering perspective.
