The nervous system consists mainly of two types of cells, neurons and glial cells. Glial cells are further divided into three different classes: schwann cells and oligodendrocytes, astrocytes and microglia. For a long time, glial cells were regarded as somewhat passive companions to neurons. Today, however, more than a century after their description by Virchow (1856), there is increasing evidence that neurons and glia cells have an intimate plastic morphological and functional relationship. During development of the nervous system, the interplay of neurons and glia cells is highly relevant for many different aspects. This book contains some of the latest results on glia-mediated neuronal differentiation with focus on synapse formation, dendrite development and gene regulation. One particular aspect of closer inspection is the role of glia-derived cholesterol in these processes.