South Asian region has the highest global burden of child undernutrition, with almost 41% of children stunted, 16% wasted and 33% underweight. Improved feeding of children less than 2 years of age is particularly important because they experience rapid growth and development, and are vulnerable to illnesses such as acute respiratory infections and diarrhoeal diseases. The present supplement aimed to describe complementary feeding practices in five South Asian countries - Bangladesh, India, Nepal, Pakistan and Sri Lanka - using the new and updated global complementary feeding indicators and to identify determinants of inappropriate complementary feeding practices. The South Asia Infant Feeding Research Network held a series of workshops to study and discuss the operational guidelines for the new complementary feeding indicators in consultation with regional and international experts. The latest Demographic and Health Surveys for Bangladesh, Nepal, Pakistan and Sri Lanka, and the National Family Health Survey of India were used as data sources. Four key indicators were calculated: introduction of solid, semisolid or soft foods in 6-8 months aged, minimum dietary diversity, minimum meal frequency and minimum acceptable diet in 6-23-month-aged children. Univariate and multivariate logistic regression analyses were performed to identify determinants of poor complementary feeding practices. The papers in this supplement present results of these analyses for each individual country and a comparison between countries. The results have important implications for policies, programmes and research on infant and young child feeding in the region, especially for targeting groups at high risk for suboptimal practices.