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Renewability and the carbonaceous basis of biomass provide potential for both energy and chemical production in biorefineries in a fashion similar to crude oil refineries. Biorefineries are envisaged as having a key role in the transition to a more sustainable industry, especially as a means to mitigate greenhouse gas (GHG) emissions. A biorefinery is a concept for the flexible, efficient, cost-effective and sustainable conversion of biomass through a combination of process technologies into multiple products. This implies that biorefineries must be integrated through designs that exploit the interactions between material and energy streams. The wide range of possibilities for biomass feedstock, processes and products poses a challenge to biorefinery design. Integrating biorefineries within evolving economic and environmental policy contexts requires careful analysis of the configurations to be deployed from early in the design stage. This research therefore focuses on the application and development of methodologies for biorefinery design encompassing process integration tools, economic and environmental sustainability analyses together. The research is presented in the form of papers published or submitted to relevant peer-reviewed journals, with a preamble for each paper and a final synthesis of the work as a whole. In a first stage, mass pinch analysis was adapted into a method for integration ofbiorefineries producing bioethanol as a final product and also utilising bioethanol asa working fluid within the biorefinery. The tool allows targeting minimum bioethanol utilisation and assessing network modifications to diminish revenue losses. This new application could stimulate the emergence of similar approaches for the design of integrated biorefineries. The thesis then moves to combine feedstock production models, process simulations in Aspen Plus® and process integration with LCA, to improve energy efficiency and reduce GHG emissions of biorefineries. This work, presented via two publications covering wheat to bioethanol and Jatropha to biodiesel or green diesel, provided evidence of the benefits of biorefinery integrationfor energy saving and climate change adaptation. The multilevel modelling approach is then further integrated into a methodologydeveloped for the combined evaluation of the economic potential and GHG emissions saving of a biorefinery from the marginal performances of biorefineryproducts. The tool allows assessing process integration pathways and targeting forpolicy compliance. The tool is presented via two further publications, the first drawing analogies between value analysis and environmental impact analysis inorder to create the combined Economic Value and Environmental Impact (EVEI)analysis methodology, the second extending this to demonstrate how the tool canguide judicious movement of environmental burdens to meet policy targets. The research embodied in this thesis forms a systematic basis for the analysis andgeneration of biorefinery process designs for enhanced sustainability. The toolspresented will facilitate both the implementation of integrated biorefinery designsand the cultivation of a community of biorefinery engineers for whom suchintegrated thinking is their distinctive and defining attribute.