Project B09 analyzes whether and how professional networks facilitate international migration. Professional networks are key to transmit migration-relevant information (e.g. about job perspectives or everyday life in the destination). Therefore, they potentially correct or reinforce biases in individual beliefs which influences the migration decision. The project studies the role of professional networks from a historical and a contemporaneous perspective. In both perspectives, professional networks are measured at an unprecedented level of detail. For the historical perspective, it is asked how networks affected the emigration of Jewish high-skilled individuals from Nazi Germany, one of the largest emigration waves of high-skilled individuals in history. For the contemporaneous perspective, large online databases are analyzed that allow investigating professional networks and international migration decisions of high-skilled individuals with contemporaneous data.