The document is a guidebook for using the Malnutrition Universal Screening Tool (MUST) to screen adults for malnutrition risk. It estimates that over 3 million people in the UK are at risk of malnutrition based on nutrition screening week surveys that found 28-42% of hospital and care home patients to be at medium or high risk. Malnutrition has significant health, social care, and economic costs due to consequences like impaired immune function and wound healing, reduced muscle strength, and increased risk of falls and hospital admissions. The MUST tool and guidebook aim to improve malnutrition screening and care planning.