Over the last 10 years, budget monitoring and analysis have grown enormously in popularity as a tool for holding the government to account at all levels – from the national to the grassroots. Equally, budget monitoring can be a tool for monitoring the activities of donors – holding them to commitments or exposing gaps between their advice or conditionalities and their own practice. Save the Children UK has a long track record of lobbying for improved services for children around the world and of working with the public sector to improve implementation, accessibility, and relevance of services. As the public expenditure is central to providing key services for protecting children’s rights and wellbeing, several Save the Children UK programmes are carrying out budget monitoring activities. This publication draws together lessons from this widely varied work. This 30-page paper presents various case studies in Ghana, India, Mozambique, South America, and Wales.