Adequate nutrition during the first 1,000 days is necessary for children to grow and develop to their full potential. Alive & Thrive (A&T) contributes to better nutrition during the first 1,000 days by promoting improved infant and young child feeding (IYCF) practices. A&T is expanding its efforts to Nigeria and will target Lagos and Kaduna States. In Nigeria, 33% of infants are breastfed within 1 hour of delivery, 60% are given other fluids in the first 3 days of life, and only 17% of children 0-5.9 months are exclusively breastfed. Approximately 60% of children 6 to 23 months achieve the minimum meal frequency for their age and 19% are fed four or more food groups per day. To address these gaps in optimal IYCF practices, A&T will use an implementation framework for IYCF impact at scale that includes advocacy, interpersonal communication and community mobilization, mass communication, and strategic use of data. The A&T intervention will be compared to mass media communication on IYCF, which will be provided throughout the two states. LGAs in Lagos and Kaduna will be randomly allocated such that two-thirds receive the A&T intervention and one-third are assigned to the comparison group. The primary objectives of the evaluation are to measure the impact of the A&T intervention on IYCF practices among mothers with children 0-23 months of age overall, in each state, and in a subset of urban LGAs. Secondary evaluation objectives are to document: the type, quantity, and timing of the implementation of A&T program activities; coverage levels A&T achieves with different program activities; extent to which A&T increases knowledge and awareness of optimal IYCF practices among women with children 0 to 23 months and health providers; extent to which A&T improves the capacity of health providers to counsel mothers on IYCF; and extent to which A&T improves the capacity of stakeholders to implement community-based activities that support optimal IYCF practices.