In this article, we give an overview of these items and discuss the associated technological trends. In the first section, the history of wearable electronics is summarized, with special emphasis on I/O systems and substrate and packaging issues. Interconnections for wearable devices are introduced in the second section; they can be split into wireline and wireless approaches, as well as permanent versus detachable connections. In the third section, wearable health care systems on a chip (SoCs) and systems on textiles (SoTs) are explained in connection with their appropriate applications. Since wearable health care applications are a good match with wearable technologies, most of the dedicated chips have been developed for health care monitoring, diagnosis, and treatment. A final section presents anumber of conclusions regarding wearable electronics.