  Biological systems, from a cell to the human brain, are inherently complex. A
powerful representation of such systems, described by an intricate web of
relationships across multiple scales, is provided by complex networks.
Recently, several studies are highlighting how simple networks -- obtained by
aggregating or neglecting temporal or categorical description of biological
data -- are not able to account for the richness of information characterizing
biological systems. More complex models, namely multilayer networks, are needed
to account for interdependencies, often varying across time, of biological
interacting units within a cell, a tissue or parts of an organism.
