ArgumentThis paper considers some aspects of the reception and development of contemporary mathematics in Spain during the first half of the twentieth century, more specifically between 1910 and 1950. It analyzes the possible influence of scientists’ mobility in the adoption of newer views or theories. A short overview of key points of the social and scientific background in nineteenth-century Spain locates the expounded facts in an appropriate context. Three leading threads are followed. First is the consideration of the mobility of some Spanish mathematicians during a period including World War I and World War II – when Spain was a theoretically neutral country – and the Spanish Civil War (1936–1939). Second, the emergence and socio-political behavior of a dominant mathematical group gathered around Julio Rey Pastor between 1915 and 1936 is also accounted for, as well as its continuity after the Civil War into the 1940s. Third, attention is paid to the migration or interior exile of a number of mathematicians as a consequence of the Civil War. The paper is organized around nine Tables containing information on mobility of mathematicians, doctorates awarded in the mathematical sciences, and mathematical production in Spain during this period, accompanied by statistical résumés and comments on interesting entries. The main conclusions drawn are: 1) a number of integrants of the Rey group, himself included, officially traveled to Austria, France, Germany, Italy, and Switzerland – usually after having obtained doctorates and fixed positions – imported mathematical knowledge into Spain; 2) the group also managed to dominate the mathematical panorama from both the scientific and the sociological viewpoint; 3) social usages in Spanish mathematical affairs established in Spain in the years prior to the Civil War present a clear continuity under the Franco regime once the war was over.