On many aspects of human development, the gaps between different groups of people continue to widen. ‘Leave no one behind’ (LNOB) is a commitment made by United Nations (UN) Member States to eradicate poverty, reduce inequalities and end discrimination. It prioritises the most vulnerable and marginalised members of society, and is at the heart of the Sustainable Development Goals (SDGs). The UN General Assembly specifically mandates UNICEF to advocate for the protection of children’s rights, to help meet their basic needs and to expand their opportunities so they can reach their full potential. The LNOB imperative at UNICEF is founded on the Convention of the Rights of the Child, and the recognition of the Human Rights to Water and Sanitation, and must be pivotal for all UNICEF water, sanitation and hygiene (WASH) programming. LNOB is not optional for UNICEF. It is not aspirational, or something that should be viewed as an add-on. Rather, it must be fully embedded in the way that UNICEF and its partners work.