Our knowledge of the causes of brain tumors has steadily increased and is leading to a refined understanding of the signaling pathways that may be essential for tumor formation. At the same time, we are gaining insights into the developmental processes that regulate the formation of the diverse range of cell types in the normal brain. Interestingly, many of these pathways seem to overlap and suggest common mechanisms regulating tumor formation and cellular development. This overlap may also inform us about the nature of the cell of origin for different types of brain tumors. By appreciating the inter-relationship between tumor formation and development, we may be able to design new therapeutics targeting tumors for new modes of treatment.