Carbon monoxide (CO) is a gasotransmitter that plays important roles in regulating cell functions and has shown therapeutic effects in clinic studies. CO releasing molecules (CORMs), which allow controlled release of CO in physiological conditions, have been intensively studied in the past decade. While most CORMs are metal complexes, several nonmetallic CORMs have also been developed and most of them were reported in recent years. The major advantages of nonmetallic CORMs are potentially low toxicity and easy modification for property tuning. Syntheses, CO-release mechanisms, biological behaviors, and physicochemical properties of these nonmetallic CORMs are reviewed here. The first part of this short review covers the nonmetallic CORMs that do not require irradiation to release CO, which includes methylene chloride, CORM-A1 and its derivatives, amine carboxyboranes, and bimolecular CORMs. The second part focuses on the CORMs that release CO under irradiation (PhotoCORMs) including unsaturated cyclic diketones, xanthene carboxylic acids, meso-carboxy BODIPYs, and hydroxyflavones. Future prospects are discussed at the end of this review.