The use of mathematical tools to study biological systems has a long history, with such milestones as the Lotka-Volterra model (Lotka 1910), the mathematics of enzyme kinetics (Michaelis and Menten 1913), the Hodgkin-Huxley model of action potentials in neurons (Hodgkin et al. 1952), and Turing's theory of morphogenesis (Turing 1952). Traditionally, the principal tool of the mathematical biologist was the differential equation, which provides models of a variety of dynamic processes, with many applications, in particular in population dynamics, one of the few areas of biology where some quantitative data were available to calibrate models to reality. This lack of suitable data to build realistic quantitative dynamic models was an important reason why mathematical biology was not able to reach its full potential during most of the 20th century. This was to change dramatically with the advent of the technological revolution in molecular biology that began in the 1970s with DNA sequencing machines and in the 1990s with DNA microarrays. Population biology also benefited from better data collection technologies. Ever-improving in vivo imaging methods promise similar advances at the tissue and organ levels for mammals. In genetics and genomics we are now in a position where data generation capabilities have far outstripped the capabilities of analyzing them, both for lack of appropriate algorithms and lack of suitable hardware. Also, entirely new higher quality data types are becoming available, such as CHIP-seq molecular data or measurements of single-cell protein concentrations. With new data types and larger data quantities, new problems can be approached with mathematical methods. Systems biology applies principles from mathematical systems theory to biological systems and networks whose components we can now measure on a large scale. Evolutionary biology benefits from the R. Laubenbacher ( )