For four years, MIT bioengineer Linda Griffith has been slowly unraveling the biology of endometriosis, a complicated and poorly understood disease that she has silently struggled with her entire life. The condition—in which tissue normally found in the uterus grows elsewhere in the body—is remarkably common. It causes severe pain and infertility and affects up to 10 percent of women, yet relatively little is known about what causes it, how to prevent it, or even how to effectively treat it.