  We introduce a model for dynamic networks, where the links or the strengths
of the links change over time. We solve the model by mapping dynamic networks
to the problem of directed percolation, where the direction corresponds to the
evolution of the network in time. We show that the dynamic network undergoes a
percolation phase transition at a critical concentration $p_c$, which decreases
with the rate $r$ at which the network links are changed. The behavior near
criticality is universal and independent of $r$. We find fundamental network
laws are changed. (i) For Erd\H{o}s-R\'{e}nyi networks we find that the size of
the giant component at criticality scales with the network size $N$ for all
values of $r$, rather than as $N^{2/3}$. (ii) In the presence of a broad
distribution of disorder, the optimal path length between two nodes in a
dynamic network scales as $N^{1/2}$, compared to $N^{1/3}$ in a static network.
