Artificial manipulation of DNA, with its attendant promise and choices, is now a reality. This technology is made possible by insights into a natural process that occurs within every functioning cell. Every day a human cell is subject to approximately 70,000 lesions from various sources. Cells have amazing mechanisms to almost always repair these lesions, and damage to DNA that goes unrepaired contributes directly to cancer and aging. We’ll look at how these natural mechanisms of DNA breakage and repair lead directly to modern methods that intentionally break DNA at defined locations and then repair it in a targeted way to provide cells with new or augmented functions.