Vermicomposting is a process where organic wastes are degraded through the earthworm–microorganisms synergistic relationship. Although vermicomposting effectively reduces organic biomass and in turn generates quality bio-fertilizers required for plant growth and soil improvement, there is sparse knowledge about the microbial communities involved in the decomposition process. On the basis of habitats, sizes, and feeding habits, vermicompost earthworms are divided into epigeic, anecic, and endogeic, with the epigeic earthworms being a better option for vermicomposting as a result of their rapid conversion of organic matter to vermicast. The vermicast of earthworms is a high-quality nutrient-rich fertilizer containing nitrogen-fixing bacteria, auxin, gibberellin, micronutrients, beneficial microbes, phosphate-solubilizing bacteria, humus, and nitrogen, phosphorus, and potassium (NPK). Microorganisms involved in vermicompost are bacteria, fungi, and actinomycetes, with soil improvement and plant protection capacities. The positive impact of the symbiotic relationship between earthworms and microorganisms has been recognized. The earthworm’s ability to degrade organic matter is ascribed to the microbial communities residing in the gut of the earthworms and in turn establishes a suitable environment through aeration, burrowing, secretion, and cast for an enhanced microbial activity. In view of these, this chapter highlights the biotic and abiotic components of vermicompost, phases involved in the vermicompost process, and the symbiotic relationship of earthworms and some groups of microorganisms.