Imagine a discipline of cellular engineering that tailor-makes biological cells to function as sensors and actuators, as programmable delivery vehicles for pharmaceuticals, or as chemical factories for the assembly of nanoscale structures. The ability to fabricate such systems seems within our reach, even if it is not yet within our grasp. Yet fabrication is only part of the story. Digital computers have always been constructed to behave as precise arrangements of reliable parts, and almost all techniques for organizing computations depend on this precision and reliability. We can envision producing vast quantities of individual computing elements—whether microfabricated particles or engineered cells—but we have few ideas for programming them effectively. The opportunity to exploit these new technologies poses a broad conceptual challenge—the challenge of amorphous computing. How can prespecified, coherent behavior be engineered from the cooperation of vast numbers of unreliable parts interconnected in unknown, irregular, and time-varying ways? One critical task is to identify appropriate organizing principles and programming methodologies for controlling amorphous systems. The growth of form in biological organisms demonstrates that welldefined shapes and functional structures can develop through the interaction of cells under the control of a genetic program, even though the precise arrangements and numbers of the individual cells are variable. Accordingly, we discuss some ideas for controlling amorphous systems, especially the hints from biology. We turn to biology not just as a metaphor, but as an actual implementation technology for amorphous systems by means of “cellular computing,” which constructs logic circuits within living cells.