The high hereditary factor of Bipolar Disorder has been proven by many twin-, adoption- and family-studies already decades ago. Concordance rates between monozygotic twins are even as high as 40-70%. Children of two affected parents have a lifetime-risk of 50-65% to fall ill with Bipolar Disorder, while children with one affected parent show a risk of 25% to get Bipolar Disorder. Therefore psychiatric genetics is highly important to detect the genetic blueprint of Bipolar Disorder to invent prevention strategies, as well as individualized pharmacotherapy and new medication targets. Interestingly top susceptibility genes belong to the ion channel group, growth hormones, clock genes, neurotransmitter systems, Lithium sensitive pathway and other important groups. A detailed and exciting description is given by the authors within this book. Furthermore basic principles of genetics, gene-environment-interactions and genetic overlaps between psychiatric diseases are described to picture the whole painting of Genetics of Bipolar Disorder.