Neurology does not include study of the limbic system as this is regarded as more relevant to psychiatry. Paradoxically, psychiatrists receive no education on the anatomy, physiology or neuropathology of the limbic system either during their specialist training programs internationally. Their focus is purely on the diagnosis and treatment of mental illness. Thus, they are unique among the medical specialities in the 21^st century. The morbidity and mortality of the many millions of patients with mood disorders has remained unchanged for multiple decades, as opposed to the progressive advances made in all other medical specialities. This is a travesty and a tragedy for a medical specialist discipline. Accordingly, using advances in immunology, radiology and my own personal insights, and after considerable research, I have discovered the complex neuropathogenesis of mood disorders and how to substantially improve the treatment regimen in order to substantially improve patient outcomes. A detailed, comprehensive description of the anatomy, physiology, the neuropathology of the limbic system and the underlying etiology of mood disorders are described in this book. It is likely that a team approach using a psychiatrist and an immunologist will be required for patients with bipolar 2 and treatment resistant depression as the use of biological agents are complex and require considerable experience.