AbstractObjectiveTo systematically review the design, implementation and effectiveness of mass media and nutrition education interventions for improving infant and young child feeding (IYCF) practices and related psychosocial factors.DesignA search of PubMed, Embase and PsycINFO databases, a Google search, and a consultation with experts in the field of IYCF performed in July 2016.SettingLow- and middle-income countries, as defined by the World Bank Group.SubjectsEligible studies: included a mass media component (with or without nutrition education); conducted a pre–post evaluation (with or without a control group); assessed IYCF knowledge, attitudes, beliefs and/or practices; and were published in English between 2000 and present.ResultsEighteen unique studies were identified that examined the effect of mass media (types included: television; print; voice and/or SMS (text) messages; radio; megaphones/loudspeakers; videos; social media; songs/dramas) and nutrition education interventions on IYCF practices within thirteen countries. Of these, fifteen studies reported improvements in breast- and/or complementary feeding practices, using indicators recommended by the WHO, and six studies reported improvements in related psychosocial factors. However, little detail was provided on the use of formative research, a formal behaviour change theory and behaviour change techniques. Few studies reported both dose delivered and participants’ exposure to the intervention.ConclusionsDespite evidence of effectiveness, few common elements in the design of interventions were identified. Future research should consistently report these details to open the ‘black box’ of IYCF interventions, identify effective design components and ensure replicability.