The sharing economy has changed the nature of how we procure goods and services, with implications for physical resources and emissions that affect our environment and our health. Through an examination of sharing across three sectors – transportation, housing, and goods – this chapter describes how sharing platforms influence the physical economy. In some cases, sharing appears to fulfil its promise of reducing material consumption and emissions through pooled demand, but in other cases, systems-level effects can lead to increases in resource demands, emissions, and environmental impacts. Based on these potential trade-offs, we advocate for four measures that improve the environmental outcomes of sharing platforms: (1) Design algorithms to emphasize proximity; (2) Encourage low-carbon transportation options for sharing transactions; (3) Model the system and mitigate unintended effects; and (4) Focus sharing on transactions with the highest environmental benefits. Finally, there are additional opportunities for sharing platforms to effect positive environmental change through research, by harnessing their data to answer important environmental engineering and policy questions.