In the developing central nervous system (CNS), neural stem cells undergo a complex series of �morphogenetic and motile events. Errors in neural stem cell proliferation or migration cause serious brain developmental disorders. However, the relative importance of each step in neurogenesis and migration and the identity of genes affecting these processes has only begun to be explored. Using live imaging in brain slices, neural stem cells and their progeny labeled by in utero gene transfer can be monitored at high spatial and temporal resolution for as long as several days. Cell cycle progression, mitosis, morphogenesis, and migratory behavior can each be documented in detail. Furthermore, the behavior of subcellular structures, including nuclei, centrosomes, and microtubules, can also be observed using fluorescent marker proteins. This chapter describes the application of these approaches in combination with RNA interference to investigate normal developing brain and the role of genes involved in brain developmental disorders, such as lissencephaly.