First published in 1957. This is Volume VIII of Mannheim's collected works. When Karl Mannheim was proscribed by Hitler in 1933, like others on that first list he was at once offered academic posts in universities in different parts of the world. He came to London, and the book which follows is based on two of the courses of lectures that he gave in London: the first was given at the London School of Economics under the title Systematic Sociology, and the second elsewhere under the title Social Structure. The first three parts of this book are based on the manuscript of Mannheim's lectures on systematic sociology, first delivered during the academic session 1934-35 and, in slightly modified form, during the following sessions. Part Four of this book is based on some of the lectures in a course on social structure delivered during the war years.