The global demand for resources is escalating in todayâs rapidly evolving world. As traditional raw materials become scarcer and more expensive, alternative sources have to be found. One such emerging resource is oil shale ash. This article provides a comprehensive overview of the various fractions of oil shale ash generated in the oil shale industry in Estonia. The ash results from the direct combustion of oil shale with pulverised combustion (PC) and circulating fluidised bed combustion (CFBC) technologies, as well as from shale oil production processes. It offers detailed information about the proportions of ash derived from different technological processes and a thorough analysis of their mineralogical and chemical compositions, trace element content, and leaching characteristics. By examining these diverse characteristics, the study enhances understanding of the ashâs potential implications and applications.