Editorial The last decade has seen a dramatic change in the status of mathematical methods in biology. The usefulness of mathematics in providing a deeper insight into the organization of fundamental biological processes is now widely recognized. Many areas of modern biology are becoming increasingly quantitative. In my opinion, however, this process is far from optimal. There is still a tangible proportion of ad hoc methods lacking theoretical underpinnings and/or rigorous testing. Biological systems are extraordinarily complex, calling for methods that are commensurate with this complexity. Modern mathematics offers a much richer arsenal of tools and ideas than those that are frequently employed to describe the enormous diversity of biological phenomena. This does not imply that all methods of data analysis should necessarily be sophisticated but they must meet a much higher standard of scientific rigor than is currently the case. The new Mathematical Biology section of Biology Direct is intended to help set such a standard.