The ENFiber D3 deliverable, led by Working Group 1, presents the Month-12 Database of Fiber Sources. It compiles the compositional profiles and preliminary feasibility screening of 29 plant-based food processing by-products, grouped into seed, fruit and vegetable by-products, as potential sources of dietary fiber. The data are drawn from peer-reviewed literature and unpublished contributions from WG1 members. The deliverable identifies priority by-products for further extraction feasibility and sustainability assessments in the next phase of the Action. This database is a dynamic resource that will be continuously updated as new evidence and additional by-products become available. Ultimately, the collected information will be integrated into the ENFiber Fiber Portal, an online platform designed to facilitate access to information on fiber sources and support knowledge exchange, research collaboration and sustainable fiber valorisation.