There are many excellent publications outlining features of assessment and feedback design in higher education. However, university educators often find these ideas challenging to realise in practice, as much of the literature focuses on institutional change rather than supporting academics. This paper describes the conceptual development of a practical framework designed to stimulate educators' thinking when creating or modifying assessments. We explain the concepts that underpin this practical support, including the notions of "assessment decisions" and "assessment design phases", as informed by relevant literature and empirical data. We also present the outcome of this work. The Assessment Design Decisions Framework. This provides key considerations in six categories: purposes, contexts, tasks, interactions, feedback processes and learning outcomes. By tracing the development of the Framework, we highlight complex ways of thinking about assessment that are relevant to those who design and deliver assessment to tertiary students.