The rising research interest in personalized medicine promises to revolutionize traditional medical practices. This presents a tremendous opportunity for developing wearable devices toward predictive analytics and treatment. In this talk, I will introduce our recent advances in developing fully-integrated skin-interfaced flexible biosensors for non-invasive molecular analysis. Such wearable biosensors can continuously, selectively, and accurately measure a wide spectrum of sweat analytes including metabolites, electrolytes, hormones, drugs, and other small molecules. These devices also allow us to gain real-time insight into the sweat secretion and gland physiology. The clinical value of our wearable sensing platforms is evaluated through multiple human studies involving both healthy and patient populations toward physiological monitoring, disease diagnosis, and drug monitoring. This talk will also feature our very recent works on laser-engraved lab on the skin and biofuel powered battery-free electronic skin toward metabolic/nutritional management as well as dynamic stress monitoring. These wearable and flexible devices could open the door to a wide range of personalized monitoring, diagnostic, and therapeutic applications.