Imagine popping a movie into the VCR or DVD player and watching a list of credits for two hours—no movie, no plot, no dialogue—just the cast. That’s the problem facing contemporary biology. The human genome project has provided researchers with a growing list of genes—basically a cast of thousands of characters, running life inside the cell. But the key to understanding life, both in health and sickness, is the script that outlines how these cellular players interact, communicate, and cue each other.