Wearable and mobile health technology is becoming increasingly pervasive, both in professional healthcare settings and with individual consumers. This chapter delineates the various functionalities of this technology and identifies its different purposes. It then addresses the ethical challenges that this pervasiveness poses in the areas of accuracy and reliability of the technology, privacy and confidentiality of data, consent, and the democratization of healthcare. It also looks at mobile mental health apps as a case study to elucidate the discussion of ethical issues. Finally, the chapter turns to the question of how this technology and the associated “quantification of the self” affect traditional modes of epistemic access to and phenomenological conceptions of the self.