In this lecture we consider hyperbolic partial differential equations on
networks. We give an overview on such problems in civil engineering and
structural mechanics, including gas networks, waste- and fresh water
networks as well as mechanical flexible multi-structures.
Typically, the applications have a genuine multiscale character and
require rather complex modeling and simulation ranging from discrete to
continuum models. In the second part of the talk we take a particular
network  model, namely, a network of fully nonlinear strings in 3-D,
analyze the model for individual strings, discuss the network model,
provide existence of semi-global solutions and discuss exact
controllability of a tree-like network. We also provide some numerical
approach to network problems. More details might be handled in a
forthcoming lecture.