Bioleaching is an economical process to extract rare earth elements, which requires less energyand produces less toxic gases than chemical extraction methods. However, the extraction efficiency varies with different parameters. Bioleaching mechanisms, as well as factors controlling the process, were comprehensively analyzed in this study. The quantitative analysis will help optimize bioleaching process parameters for the high co-extraction of metals. Analyzing 61 peer-reviewed articles on bioleaching, we identified three main factors that affect the bioleaching mechanism — microorganism type, source type, and specific REE. Extraction efficiency varies between 0 to 100% based on the condition used in the study. Among different types of microorganisms used to extract REE, fungi were found to have a competitive advantage over other microorganisms such as chemolithoautotrophs or heterotrophs. Primary and secondary sources of REE are typically used for extraction. Among them, electronic waste leaches more REE per unit mass of source reacted, irrespective of the microorganism type. Extraction efficiencies of transition metals were higher than those of REEs