"Flow" is a book that examines the core question of: How can financial systems open flow of finance for all? An impediment to delivering sustainable development is that finance is not flowing to everywhere that it is needed. "Flow" unpacks why this is the case, and what we can do about it. This is a book about hope. In the end, the book comes down to a single proposition captured in a single word. Flow. It is the flow of finance to all that ultimately impacts societies and our environment. Flow is the measure by which we understand whether a financial system is serving society. A world where finance does not flow is a world of heightened systemic risks from mass migration of peoples through to unabated climate change. There is a tendency to think that finance is complicated. Books about finance must therefore only be for those that either understand, or want to understand, the intricacies of financial markets. This is not true. Finance at its heart is very simple. Two types of finance - debt and equity - make up the foundations of modern finance. What is complicated is the way that we commonly talk about finance. The approach with this book is to tell the story of the power of finance through narratives. The analogy used throughout the book is that finance is like water. Just as water will find a way to flow to its level, so too can finance-if we allow it to. The core thesis of the book is that just as human intervention created the canals that flowed water to where it was needed in ancient civilizations, there is a need for intervention to support the establishment of "finance canals" that will open a flow of finance for all. The book is focused on solutions. Finance can grow businesses that can improve the standard of living across the globe. Finance can support governments to address some of the most fundamental challenges facing humanity including climate change. Finance can unlock investments that protect, preserve, and regenerate our environment. The changes advocated to open a flow of finance to meet the needs of all are practical and achievable without the need for international treaties or changes to domestic legislation. Flow of finance for all is about creating and maintaining the channels that enable finance to reach every corner of the earth and fulfil every need.