Actin microfilaments play a direct role in a variety of cell processes. Distinct populations of microfilaments are associated with different cellular compartments, such as growth cones, filipodia, stress fibers, and lamellipodia. It is becoming clear that these different populations are often composed of different isoforms of the two core microfilament components, actin and tropomyosin. This is particularly true in neurons, where actin and tropomyosin isoforms are segregated into different intracellular compartments which correspond to functionally distinct regions of the neuron. Developmental regulation of this isoform sorting suggests a specific role for some isoforms in growth and for others in stabilization of neuronal structure. This provides a mechanism by which a neuron can create and independently regulate intracellular domains composed of microfilaments with different functional properties.