More than eighty years ago now Smith and Townsend published an article in which they presented evidence that the bacterium which is now called Agrobacterium tumefaciens is the causative agent of the widespread neoplastic plant disease crown gall. Since then a large number of scientists throughout the world have focused their research on this organism in a effort to analyze the molecular mechanism underlying the process of crown gall induction in detail.  This was driven by the hope that this would lead to a better understanding of oncogenesis in general, and to the development of remedies for such diseases.  After a period of diminished interest in the system Agrobacterium and crown gall research revived when it became apparent that oncogenic gene transfer from Agrobacterium to plants might form the molecular basis  of crown gall induction, and thus the transfer system might be exploited for the genetic engineering of plants.