Recent technological and methodological advances have seen a rapid increase in the development and use of wearable technologies, advancing the study and practice of precision health for individuals across real-world contexts and health statuses. This narrative review highlights the recent scientific advances and emerging challenges of wearable technologies. We first review the advantages of monitoring physical activity using wearable technologies over self-reports and examine commercially available devices' reliability and validity. Next, we point to the utility of wearable technologies in naturalistic environments to examine temporal associations between physical activity with other health behaviors, psychological processes, and ambulatory markers of disease that can inform the clinical practice of precision health. We further identify studies that use wearable technologies to facilitate behavior change across different populations, highlighting the need to adapt interventions for different individuals, contexts, and disorders. Balanced against these opportunities, we also highlight several challenges facing the field of precision monitoring. (PsycInfo Database Record (c) 2021 APA, all rights reserved).