Histological classification and staging are cornerstones of diagnosis in lung cancer. Treatment options have been enriched in the last few years by the development of a number of new drugs, and therapy is now increasingly being carried out within multimodal concepts and at earlier stages. Still, outcome of the disease is far from satisfactory and progress in clinical and preclinical research is time-consuming. With the whole variety of potent new therapeutic compounds including classical cytostatics and biological factors at hand, many now believe that a clear improvement of treatment results will be derived from a better understanding of the biology of these tumours and a resulting improvement of diagnosis. Biological factors reflecting the underlying tumour biology and aspects of clinically important pathomechanisms may not only better predict outcome of the disease but also of its treatment, serving as surrogate markers for a more appropriate general intensification of therapy and ideally for specific "targeted" interventions. This article describes the different insights in the biology of these tumours in relation with the representing surrogate markers, and opens routes to possible diagnostic and therapeutic consequences.