Diarrhea and acute respiratory infections account for nearly 30% of deaths among children displaced by humanitarian emergencies. Handwashing with soap reduces the risk of diarrhea and acute respiratory infection in non-emergency settings. However, the practice and the effectiveness of handwashing promotion efforts and the health benefits are not well documented in emergency settings. We conducted key informant interviews with 12 experts working in water, sanitation, and hygiene and examined current approaches, challenges, and knowledge gaps in relation to handwashing promotion in emergency settings. We identified many constraints to implementing effective handwashing promotion efforts including a failure to define objectives and targets for improvements in handwashing rates, lack of technical expertise and attention to the development and implementation of effective behavior change communication approaches, and limited understanding of the appropriateness, use, and acceptability of different handwashing hardware. Respondents identified multiple knowledge gaps and research needs that could improve current efforts. Collaborations between response agencies and research institutions could generate high quality data and facilitate contextualized and potentially more effective and robust handwashing promotion strategies.