The document provides an analysis of the economics of co-firing rice straw with coal in Vietnam's coal power plants, considering both old and new facilities. It explores the economic, social, environmental, and policy drivers for considering biomass energy, particularly the potential for fuel cost savings, job creation in rural areas, reduction in air pollutant emissions, and GHG emission mitigation. The study uses a financial model to evaluate the viability of co-firing, taking into account factors such as willingness to accept/pay and the external benefits of improved local air quality. Two case studies, Mong Duong 1 (a new plant) and Ninh Binh (an old plant), are examined to assess the job creation potential, impact on national trade balance, and environmental benefits of co-firing. The findings suggest that co-firing can provide significant benefits in terms of local air quality, which could justify the technology beyond the greenhouse gas emissions reductions, and it is recommended to implement Renewable Portfolio Standards in Vietnam.