Wearable systems offer great promise in application domains as varied as healthcare, eldercare, augmented work, education, athletics, entertainment, parenting, travel, and personal productivity. In this keynote lecture I outline some of these opportunities and identify some of the many challenges we face in developing wearable technology that realize those opportunities. Notably, I anticipate wearable technology raising significant security risks and privacy issues--challenges we must address as we design and develop wearable devices, systems, and applications if we hope to see this technology widely accepted and adopted. Strong (and usable) security mechanisms are essential for safety-critical applications; meaningful privacy protections are essential for systems that accompany us through our private and public life. By raising these concerns today, I seek to ensure the wearable systems of tomorrow will have strong and usable security and privacy properties.