The assessment of bio based products presents several challenges: from the definition of system boundaries and choice of system models, modeling competition for biomass and for land, to performing dynamic and time specific accounting, making scenarios and considering uncertainty. We present the background, methodology, and expected results of the Horizon-Europe-funded project “Aligning Life Cycle Assessment methods and bio-based sectors for improved environmental performance” (ALIGNED, grant number 101059430). Targeting five sectors namely woodworking, pulp and paper, biochemicals, construction and textiles, ALIGNED fulfils three research needs: 1) to improve, harmonize, and align LCA methodology for the assessment of bio-based products covering environmental and socio-economic aspects, 2) to demonstrate the harmonized methodology to improve the environmental performance of specific technology development cases in industries within the bio-based sectors 3) to inform and involve stakeholders, enabling an efficient methodological uptake.ALIGNED modelling framework does not intend to provide a new standard or guideline but instead to make available an ecosystem of science-based and open approaches and tools to ease the assessment of bio-based products. Key elements in such framework include: 1) A science and evidence-based approach: scientifically sound modelling as close as possible to reality, avoiding normative rules, and favoring models that can be validated and revised when new data become available as well as an ecosystem of interacting models and tools. 2) A lifecycle perspective: the assessment takes the full life cycle of bio-based products into account. 3) Relevance for decision-makers and usefulness for decision support: we focus on modelling what are the consequences of specific decisions. We explicitly consider uncertainty in the decision support. 4) Balancing model complexity and model applicability: we select and use in this framework models that are scientifically robust but also usable by practitioners to the largest extent, keeping in mind the trade-off between model complexity and applicability. 5) Adherence to open-science practices: models, tools, and their documentation are open, while data should be as open as possible. 6) Ensuring relevance for bio-based products: the modelling framework considers the specific challenges and issues that exist in the assessment of bio-based products
