Bipolar disorder affects 1–2% of the population and is often associated with lifelong impaired functioning and quality of life. Bipolar disorder usually has onset at an early age and runs in families; thus, the disorder hereditary, which most people with bipolar disorders know. However, it is often difficult to understand what heredity means for their lives and, not least, their children’s lives. Since the beginning of the twentieth century, there has been a large field of research called high-risk or family studies, which deals precisely with the heritability of severe mental illness by examining family members who are first-degree relatives. There is vast interest in preventing the onset of the disease, and high-risk studies follow children and young people who have parents with bipolar disorder. This chapter will describe the main findings reported by observational studies that have followed the offspring of parents with bipolar disorder, with a primary focus on risk factors for the onset of bipolar disorder and the potential clinical implications.