Mental illness refers to a mental or behavioral pattern which causes significant interference with the functioning of a person. The behavioral patterns can be remitting, relapsing or persistent, and can occur in isolated episodes. Glial cells are important for proper functioning of neurons and dysfunction in glial cells can result in various mental illnesses, like psychiatric disorders, autism, glioblastoma and multiple sclerosis. They do not produce electrical impulses and are found in the peripheral nervous system and the central nervous system. They help homeostasis, produce myelin in the peripheral nervous system, while providing protection and support to the neurons. Glial cells comprise ependymal cells, oligodendrocytes, microglia and astrocytes in the central nervous system. They are made up of satellite cells and schwann cells in the peripheral nervous system. This book strives to provide a fair idea about glial neurobiology in mental illness and to help develop a better understanding of the latest advances in their clinical management. Those with an interest in this field would find it helpful.