Organ-on-a-chip (OoC) systems are devices that use human cells to simulate human organs - such as the liver, kidney, lung, heart, and brain - on micro-engineered chips about the size of an AA battery. This technology can help researchers examine aspects of human physiology, disease, and responses to external chemicals such as pharmaceutical drugs. Compared to other laboratory methods such as animal testing, researchers have demonstrated that OoC technologies have the potential to better model human biology, drug efficacy, and chemical toxicity. Recent legislation and agency plans - including at FDA and EPA - have called for replacing, reducing, or refining animal testing in part by developing and using more human-relevant systems, such as OoC, when possible. However, several challenges with OoC technologies remain, including the lack of acceptance of results in regulatory agencies and across industries, lack of standardization, reliable cell sourcing, and cost. Key Questions: 1) What are the current and emerging OoC technologies and what is their development status? 2) What are the potential benefits and challenges to developing or using these technologies? 3) What options, if any, could policymakers consider to help enhance the benefits or mitigate the challenges associated with OoC?