This guide sets out a practical sequence for designing and implementing feasibility studies for infrastructure projects that can be adapted to country‑specific contexts. The structure and advice draw directly on what has worked well, and what has proved challenging, in the Green Cities, Infrastructure and Energy Programme (GCIEP) which has aimed to mobilise finance while strengthening project delivery systems, sector policies and the institutional capacity of partner government entities. Evidence is drawn from GCIEP’s experience of feasibility studies in low‑ and middle‑income countries including Ghana, Indonesia and the Philippines.