Waste has attracted immense interest as a co-feedstock for sustainable biorefinery technologies, as highlighted in Chapter 6, which examines efficient conversion of waste streams into value-added bio-based products and energy carriers. The chapter gets readersstarted with an overview of conversion pathways, detailing thermochemical and biochemical pathways. Comprehensive case studies highlight success across the agricultural, municipal, and industrial sectors, including waste-to-energy projects, industrialsymbiosis collaborations, and advanced waste valorization processes. Techno-economic assessments and life cycle evaluations are underscored as crucial instruments for analyzing the practicality and sustainability of waste-derived biorefinery systems. Case studies demonstrate successful applications, reinforcing the significance of interdisciplinary cooperation among engineers, policymakers, and ecologists. By compiling present research, technological innovations, and future pathways, it offers a thorough guide for moving from traditional waste management to groundbreaking resource recovery ecosystems. It supports strengthened public–private collaborations, uniform regulations, and educational initiatives to hasten the implementation of sustainable biorefineries, ultimately aiding global decarbonization and resource resilience objectives. This document acts as an essential resource for researchers, industry participants, and policymakers dedicated to reimagining waste as a fundamental aspect of sustainable industrial metabolism.