Rare diseases pose a major challenge to patients, families, physicians, researchers, health-care systems, and to our society as a whole. A disease is considered rare when not more than one person per 2,000 people is affected. However, taking into account the vast number of almost 8,000 different rare diseases, a total number of up to 400,000 people in Austria may be affected by a rare disease - statistically speaking this corresponds to 1 in 20 people. Approximately 80 % of all rare diseases are genetically caused, but for more than half of them the genetic cause is yet poorly understood or entirely unknown. The research focus of the Ludwig Boltzmann Institute for Rare and Undiagnosed Diseases (LBI-RUD) is on rare diseases of the immune system, hematopoiesis, and the nervous system, which all together account for more than 50% of all rare diseases. Our research will not only be relevant to the affected individuals and will provide the basis for targeted therapies, but will also provide unique and novel insights into human biology far beyond the specific disease, which will add to our understanding of much more frequent diseases.