In 2004, genetic testing revealed that Masha Gessen had a mutation that predisposed her to ovarian and breast cancer. As she wrestled with a wrenching personal decision - what to do with such knowledge? - Gessen explored the landscape of this brave new world, speaking with others like her, and with experts including medical researchers, historians and religious thinkers. Blood Matters, a New York Times Notable Book for 2008, is a much needed field guide to this unfa-miliar and unsettling territory, pointing the way towards the radical transfor-mation genetic information is engineering in our sense of who we are and what we might become.