The transition toward renewable energy is a global imperative driven by rising energy demand, depletion of fossil fuel reserves, and escalating environmental concerns such as greenhouse gas emissions and climate change. Among the various renewable energy options, biofuels particularly biodiesel have emerged as promising alternatives for decarbonizing the transport and industrial sectors. However, the continued use of food-based feedstocks for biodiesel production presents sustainability challenges, including food-versus-fuel conflicts and land resource competition. This chapter addresses the pressing problem of sourcing sustainable, low-cost, and non-edible feedstocks for biodiesel production by focusing on waste frying oils (WFO), a readily available by-product of the food industry. It explores the potential of WFO as a renewable energy resource, reviewing its chemical composition, conversion pathways, and performance characteristics. The chapter critically examines key biodiesel production techniques including transesterification, pyrolysis, micro-emulsification, and dilution, with particular emphasis on the catalytic role of nanomaterials in enhancing process efficiency and fuel quality. Furthermore, it evaluates the environmental and economic benefits of WFO-based biodiesel within a circular economy framework and discusses its alignment with global Sustainable Development Goals (SDGs), particularly SDG 7 (Affordable and Clean Energy), SDG 12 (Responsible Consumption and Production), and SDG 13 (Climate Action). The chapter concludes with an economic perspective, highlighting investment costs, scalability, and policy considerations for promoting WFO-derived biodiesel as a viable contributor to the global renewable energy mix.