The document provides guidance on developing the OECD's Principles Guidance on Blended Finance. It will be developed through 2019-2020 with expert and stakeholder input. It aims to help implement the Blended Finance Principles and provide references. Key topics to be addressed include defining development objectives, assessing appropriate levels of concessionality, tailoring approaches to local context, managing risks, and evaluating results. Evidence will be built through programs focused on least developed countries, fragile contexts, water and agriculture. The guidance will align with frameworks like the SDGs, Addis Ababa Action Agenda, and enhanced DFI principles on blended concessional finance. It will take the form of a dynamic digital compendium