  We present an extension of the velocity-dependent one-scale model for cosmic
string evolution, which is suitable for describing the evolution of local and
global monopole networks. We discuss the key dynamical features that need to be
accounted for, in particular the fact that the driving force is due to the
other monopoles (rather than being due to local curvature as in the case of
extended objects) and new forms of energy loss terms due to
monopole-antimonopole capture and annihilation. For the case of local monopoles
we recover and generalize the results of Preskill, suggesting that the scaling
law for the monopole correlation length is very sensitive to the annihilation
rate. On the other hand, for global monopoles the long-range forces generically
lead to linear scaling (just like in the case of local cosmic strings). In this
case we also find good qualitative agreement between our results and the
numerical simulations of Bennett & Rhie and Yamaguchi, although future
high-resolution simulations will be needed for quantitative comparisons.
