Correspondence Kosterlitz's professional correspondence with colleagues, contemporaries, professional associations, research and funding organisations, drug companies, official bodies and others, 1940s - 1990s. This period covers most of Kosterlitz's working life in Britain, with the exception of his first few years in Aberdeen, and the correspondence contains detailed information regarding his changing research interests and career development throughout these fifty years. There is also much latent information about the international research community in which Kosterlitz worked, and his enduring relationships with others engaged in similar research or sharing the common background of German exile. 1940s - 1990s