Agro-industrial wastes and by-products are organic materials that come from a variety of processes in the agricultural and agro-processing industries. Globally, agro-industrial wastes remain under-exploited and poorly managed; many current approaches in managing agro-industrial wastes especially in third world countries culminate in environmental pollution, emission of greenhouse gases and a public health risk. Therefore, the use of microorganisms to convert these wastes into value added products (VAPs) such as biopolymers, biofuels, and enzymes, microbial protein, organic acids, antibiotics is a sustainable renewable approach to handle the above-mentioned environmental concerns. Agro-industrial wastes include field crop wastes, crop leftovers, harvest wastes, animal dung or manure, wastes from slaughterhouses and meat processing, and wastes from food preparation and consumption. Because these wastes are rich in nutrients that support microbial growth, they can be employed as substrates in different bioprocesses such as fermentation (solid state and submerged) for the production of value added products that have numerous applications in chemical, cosmetics, food, textile and pharmaceutical industries. In this chapter, we considered agro-industrial wastes and their sources, different strategies for microbial bioconversion of these wastes into VAPs, valorization pathways for diverse VAPs and examples of value-added products with their possible industrial applications.