Soil organic matter (SOM) is a key component of soil that greatly influences its structure and productivity, as well as aggregate stability. High soil aggregate stability translates to less soil erosion and hence lessens the likelihood of non-point-source water pollution. Repeated evidences of arbuscular mycorrhizal fungi increasing soil aggregate stability led to the rather accidental discovery of a soil protein called glomalin produced in abundance by the hyphae of these fungi. In the course of time, glomalin detaches from the hyphae, moves into the soil, and becomes a distinct component of the SOM. Although the structure of glomalin remains unknown to date, research has revealed that it may comprise as much as 2% of soil by weight and 30% of soil carbon. Compared to glomalin, the traditional components of SOM, humic and fulvic acids, typically average 0.1% by soil weight and 5–10% of soil carbon. Glomalin is uncommonly tough and acts as a glue to hold the soil particles together. Studies on soils from differing locations and management practices have demonstrated the overall abundance and uncommonly high stability of glomalin, as well as an overwhelming positive correlation between glomalin content and soil aggregation. Research has also identified the potential for glomalin in the role of carbon sequestration. Despite the significant amount of research that has been performed on glomalin in soils since its discovery in 1996, there is still a world of unknowns about this unique soil protein. Determining the structure of glomalin, as well as those environmental conditions that drive its presence in soils, will govern the future direction of glomalin research.