This document summarizes the key elements of the five case model used for business case development in the UK public sector: 1. The strategic case establishes the case for change and objectives, existing arrangements, business needs, scope, benefits and risks. 2. The economic case identifies critical success factors, develops a long list of options that are scoped and evaluated, and selects a preferred shortlisted option with indicative costs. 3. The commercial case covers procurement strategy, risk transfer, and contract length. 4. The financial case demonstrates affordability. 5. The management case ensures program fit and defines methodologies. Flexibility is emphasized in applying the five case model at both strategic and tactical