The fifth generation of wireless communications has driven the Internet of Things toward the upper millimeter-wave bands, where abundant spectrum enables high data rates and dense device deployment, but realizing this at scale requires nodes that are simultaneously miniature, ultra-low-power, and inexpensive to manufacture, all while overcoming the severe round-trip path loss that limits millimeter-wave backscatter. These constraints impose competing demands on millimeter-wave radio-frequency identification (mmID) devices: they must provide high gain to close the link, yet retain the wide angular coverage needed for interrogation from arbitrary reader positions. This dissertation resolves that tension along two complementary directions: additively manufactured retrodirective apertures and integrated printed sensors which both share a unified fabrication method of inkjet and 3D printing. The aperture work advances from planar to volumetric beamforming: a fully inkjet-printed, conformal transmitarray-mmID achieves wide angular coverage while remaining flexible and mechanically reconfigurable under bending, and a compact 3D-printed Luneburg lens mmID uses a stereolithography-printed isotropic truss unit cell to realize the refractive-index gradient required for near-spherical coverage, with a semi-passive, cross-polarized variant validated for long-range operation. The sensing work couples low-cost printed transducers directly to the backscatter channel through an inkjet-printed lab-on-chip mmID for liquid conductivity, a self-powered thermoelectric wearable with printed microfluidic pH sensing, a fully printed electrochemical DNA sensor for sequence-specific detection, and an amine-functionalized carbon-nanotube chemiresistor for environmental gas monitoring. Together, these contributions converge high-gain retrodirective backscatter and integrated printed sensing on one additively manufactured platform, bridging the gap between proof-of-concept mmID demonstrations and deployable low-power sensing nodes for the upper 5G regime.