  We propose a modeling framework for growing multiplexes where a node can
belong to different networks. We define new measures for multiplexes and we
identify a number of relevant ingredients for modeling their evolution such as
the coupling between the different layers and the arrival time distribution of
nodes. The topology of the multiplex changes significantly in the different
cases under consideration, with effects of the arrival time of nodes on the
degree distribution, average shortest paths and interdependence.
