In the past two decades increasing research efforts have focused on the molecular biology of the cell. In the beginning, these research activities were purely academic without any direct clinical relation. A series of important discoveries, initiated particularly by the unravelling of the genetic code and the discovery of the molecular basis of gene expression and genetics, the subsequent identification of oncogenes and tumor suppressor genes and finally the description of major mechanisms which induce genetic instability in cells, now indicate the way to many new diagnostic and therapeutic strategies. In surgical oncology, these attempts are yielding the first clinical consequences. Basic aspects of molecular cell biology as far as they are relevant for surgical oncologists are discussed.