The current presentation presents the approach followed for the derivation of the Use Cases developed in the context of ÆGIS Integrating Project (Grant Agreement: 224348) of the 7th Framework Programme, which constitute the core outputs of the user needs phase of the project, together with the Personas and the conceptual models, setting the basis for the upcoming development and evaluation phases of the project. ÆGIS aims to embed support for accessibility through the development of an Open Accessibility Framework (OAF), upon which, open source accessibility interfaces and applications for the users as well as accessibility toolkits for the developers will be built. Within ÆGIS, three mainstream markets are targeted, namely the desktop, rich Internet applications and mobile devices/applications market segments. The Use Cases developed address all three application areas, targeted by ÆGIS. The User Centred Design (UCD) plan defined from the early beginning of the initiative constituted the cornerstone of the work for the Use Cases, Personas and conceptual models. Following this plan, the project Use Cases have built on the outcomes of the field trials and the workshops (national and Pan-European), where a representative sample of all ÆGIS targeted user groups has participated and the valuable expertise of the ÆGIS Consortium members. Following a concrete development methodology, 36 Use Cases (12 for desktop, 15 for mobile and 9 for rich Internet applications), accompanied by Unified Modeling Language (UML) diagrams, 17 Personas covering all major target groups of the project and 13 conceptual models, which are mapped to the Use Cases, have emerged. The Use Cases will be further elaborated to specific application scenarios that will orient the evaluation to take place in ÆGIS in three iterative phases and across 4 Pilot sites (Belgium, Spain, Sweden and in the UK). The Use Cases are seen as working document, which may be subject to updates and revisions throughout the project, following and keeping up with the progress noticed in ÆGIS project and the overall open source accessibility community.