The tremendous advances in radio communications and ultra-low power (ULP) electronics have enabled the development of communicating biomedical sensors for the continuous monitoring of patients' physiological signals. In the last decade, much research has been done towards the advancement of wireless body area network (WBAN) technology, resulting in the release of the IEEE 802.15.6-2012 standard for the interconnection of wearable and implantable biomedical sensors. This chapter provides an overview of the sets of wireless body sensor network (WBSN) applications, as well as of their characterization parameters. One of the key requirements for widespread adoption of the WBSN technology for daily healthcare is, however, the ease of use of the sensing devices. From the patient's perspective, this means that besides being small, unobtrusive and ergonomic, WBAN nodes have to be capable of long-term operation without the need to frequently charge, recharge or even use batteries. Although the recent advances in ULP electronics have reduced the power consumption of major WBSN node components to the sub-milliwatt (sub-mW) level, the vision for uninterrupted self-powered WBANs has yet to be realized. Energy harvesting (EH), i.e. taking energy from ambient sources to power autonomous wireless networked systems, is a developing technology with a tremendous potential to complement ULP electronics towards the realization of this vision, thereby enabling the perpetual remote monitoring of a patient's vital signs. An integrated circuit (IC) that integrates most of network functionalities onto low power wearable systems has been introduced as well.