Food insecurity remains one of the most persistent global challenges, driven by rapid population growth, climate change, and constrained agricultural resources. Alongside, improper agrowaste management and the prevalent practice of crop residue burning contribute to environmental degradation and health risks. Promoting effective waste recycling and improving resource efficiency within agro-industrial sectors are therefore essential for the development of sustainable food systems. Within this context, mushroom cultivation emerges as a promising approach by serving as an efficient agrowaste management strategy and delivering socioeconomic benefits, which frames the basis for the synthesis of this chapter on sustainable bioconversion. It first examines the types and physicochemical composition of common agrowastes. Representative agrowastes and their attributes are discussed with emphasis on their relevance to mushroom cultivation, followed by insights into substrate combinations that optimize fungal growth and productivity. Biological efficiency and yield patterns are analyzed to assess cultivation performance across different agro-substrate systems. Furthermore, the recycling potential of spent mushroom substrate is explored, with attention to its applications in soil amendment, animal feed, bioenergy production, bioremediation, seed protection and mulch, and second-generation cultivation of mushrooms. Beyond technical aspects, this chapter also addresses the socioeconomic dimensions of mushroom cultivation and its role in rural livelihoods, waste repurposing, and sustainable development.