  We study the effects of friction on the scaling evolution of string networks
in condensed matter and cosmological contexts. We derive a generalized
`one-scale' model with the string correlation length $L$ and velocity $v$ as
dynamical variables. In non-relativistic systems, we obtain a well-known
$L\propto t^{1/2}$ law, showing that loop production is important. For
electroweak cosmic strings, we show transient damped epoch scaling with
$L\propto t^{5/4}$ (or, in the matter era, $L\propto t^{3/2}$). A low initial
density implies an earlier period with $L\propto t^{1/2}$. For GUT strings, the
approach to linear scaling $L\propto t$ is faster than previously estimated.
