Complementary feeding, defined as the process of providing foods in addition to milk when breast milk or milk formula alone are no longer adequate to meet nutritional requirements, generally starts at age 6 months and continues until 23 months of age, although breastfeeding may continue beyond this period (4). This is a developmental period when it is critical for children to learn to accept healthy foods and beverages and establish long-term dietary patterns (5). It also coincides with the peak period for risk of growth faltering and nutrient deficiencies (6). The immediate consequences of malnutrition during these formative years – as well as in utero and the first 6 months of life – include impaired growth, significant morbidity and mortality, and delayed motor, cognitive, and socio-emotional development. It can later lead to increased risk of noncommunicable diseases (NCDs). In the long term, undernutrition in early childhood leads to reduced work capacity and earnings and, among girls, reduced reproductive capacity (6). Inappropriate complementary feeding can result in overweight, type 2 diabetes and disability in adulthood (7). The first two years of life are also a critical period for brain development, the acquisition of language and sensory pathways for vision and hearing, and the development of higher cognitive functions (8). Purpose of the guideline This guideline provides evidence-based recommendations on complementary feeding of infants and young children 6–23 months of age living in low, middleand high-income countries. It considers the needs of both breastfed and nonbreastfed children. These are public health recommendations, recognizing that children should be managed individually so that inadequate growth, overweight, or other adverse outcomes are identified, and appropriate action taken. This guideline does not address the needs of pre-term and low-birthweight infants, children with or recovering from acute malnutrition and serious illness, children living in emergencies, or children who are disabled. Except for children with disabilities, the needs of these other groups of children are addressed in other WHO guidelines.