Electron paramagnetic resonance (EPR) is a highly accurate, extremely versatile, and efficient technique to investigate structure and electronic interactions in photovoltaic devices, catalytic materials, and semiconductors, and has also found uses in studying radiation damage, reaction monitoring, and healthcare. Though these use cases are well-developed, their applications are fundamentally limited by the traditional spectrometer, which is restricted to the laboratory due to bulky instrumentation. EPR-on-a-chip (EPRoC) integrates the performance critical components in a single microchip and minimizes the entire EPR spectrometer to a single printed circuit board that enables in situ and operando investigations in a way that is limited by neither the form factor nor the sample environment. EPRoC is comprised of a voltage-controlled oscillator (VCO) array capable of both excitation and detection of unpaired electron spins with greater spin sensitivity than conventional volume resonators. By using injection-locked VCO arrays, this sensitivity can be scaled over substantial volumes. EPRoC, when utilized with a permanent magnet, wireless communication, and a portable battery, can be used for materials and process investigations in isolated research environments such as a controlled-atmosphere glove box or in field environments such as in energy grid storage applications, solar cell installations, and to assess damage in radiation disasters. In addition to investigations and process monitoring, EPRoC is a highly quantitative device, having a rigorously defined B1 field and a well-understood spin signal response. EPRoC is capable of continuous-wave, rapid-scan, and pulse EPR methods, comprising both a highly capable spectrometer and a greatly applicable EPR sensor. Even dynamic nuclear polarization techniques are possible with EPRoC due to the intrinsically large B1 achievable and a highly scalable design that allows access to nuclear magnetic resonance enhancement in a much more power-efficient way. In this presentation, we will briefly review the EPRoC technology and focus on showcasing its versatility.