An English translation of Boveri's famous monograph which was first published in Germany in 1914. Written almost a hundred years ago, Theodor Boveri's Zur Frage der Entstehung maligner Tumoren has had a momentous impact on cancer research. In it he argues that malignancy arises as a consequence of chromosomal abnormalities and that multiplication is an inherent property of cells. With astonishing prescience, Boveri predicts in this monograph the existence of tumor suppressor mechanisms and is perhaps the first to suggest that hereditary factors (genes) are linearly arranged along chromosomes. This new translation by Sir Henry Harris, Regius Professor of Medicine Emeritus at Oxford University and former Editor-in-Chief of Journal of Cell Science, includes extensive annotations in which he discusses the relevance of Boveri's views today. It is essential reading for all cancer researchers, as well as those interested in the history of cytogenetics and cell biology.