By posing novel computational challenges and stretching the state of the art, bioinformatics has become the computing response to the molecular revolution in biology. But bioinformatics is only the first step in reshaping the life sciences. For further progress we must return to the study of whole biological systems: the heart, cardiovascular system, brain, and liver.Progress in systems biology will require computer scientists to work closely with life scientists and mathematicians. In contrast to the molecular biology revolution, computer science will actively engage in shaping systems biology. The prize to be attained is immense, ranging from in silico drug design and testing to individualized medicine that takes into account physiology and genetic profiles.