In this paper, inkjet-printed flexible antennas fabricated on paper substrates are introduced as a system-level solution for ultra-low-cost mass production of UHF radio frequency identification (RFID) tags and wireless sensor nodes (WSN) in an approach that could be easily extended to other microwave and wireless applications. The presented material is a review of our grouppsilas major reported milestones in this area. First, we discuss the benefits of using paper as a substrate for high-frequency applications, reporting its very good electrical/dielectric performance up to at least 1 GHz. The RF characteristics of the paper-based substrate are studied by using the microstrip ring resonator in order to characterize the dielectric properties (dielectric constant and loss tangent). Then, we give details about the inkjet printing technology, including the characterization of the conductive ink, which consists of nano-silver-particles, while highlighting the importance of this technology as a fast and simple fabrication technique especially on flexible organic (e.g. LCP) or paper-based substrates. A compact inkjet-printed UHF ldquopassive-RFIDrdquo antenna using the classic T-match approach and designed to match ICpsilas complex impedance, is presented as a demonstrating prototype for this technology. In addition, the author briefly touches up the state-of-the-art area of fully-integrated wireless sensor modules on paper and show the first ever 2D sensor integration with an RFID tag module on paper, as well as the possibility of a 3D multilayer paper-based RF/microwave structures. The presented approach could potentially set the foundation for the development of low-cost light-weight autonomous nodes for cognitive intelligence applications and for wearable communication and biomonitoring systems.