This paper presents a holistic and authoritative review of the role of microwave technologies in enabling a new generation of wearable devices. A human-centric Internet of Things (IoT) covering remote healthcare, distributed sensing, and consumer electronics, calls for high-performance wearable devices integrated into clothing, which require interdisciplinary research efforts to emerge. Microwaves, the "interconnect" of wireless networks, can enable, rather than solely connect, the next generation of autonomous, sustainable, and wearable-friendly electronics. First, enabling technologies including wireless power transmission and RF energy harvesting, backscattering and passive communication, RFID, and electromagnetic sensing are reviewed. We then discuss the key integration platforms, covering smart fabrics and electronic textiles, additive manufacturing, printed electronics, natively-flexible and organic RF semiconductors, and fully-integrated CMOS systems, where opportunities for hybrid integration are highlighted. The emerging This article has been accepted for inclusion in a future issue of this journal. Content is final as presented, with the exception of pagination. This article has been accepted for inclusion in a future issue of this journal. Content is final as presented, with the exception of pagination. This article has been accepted for inclusion in a future issue of this journal. Content is final as presented, with the exception of pagination. This article has been accepted for inclusion in a future issue of this journal. Content is final as presented, with the exception of pagination.