I will discuss a number of properties of cosmic string or cosmic
superstring networks with 3-way (or Y-) junctions. Such networks may be
formed in a number of different scenarios, one of which is in
brane-motivated models of inflation, and the aim is to determine their
observational consequences. First we will show that there are important
kinematic constraints on the outcome of collisions between two strings
(such collisions occur frequently during the evolution of the network).
We discuss the consequences of these, and also determine some global
properties of the network. Namely we show that at late times the lightest
tension strings are most likely to dominate the network. This conclusion
is reached via two different methods, one of which brings to light some
interesting links between string statistical mechanics and XY-models.