Neglected tropical diseases (NTDs) are a collection of diseases which are prevalent in developing countries. The diseases included by the term varies, but the World Health Organization recognizes 19 diseases, including viral, bacterial and parasitic worm infections (such as soil transmitted helminthiasis). These diseases are contrasted with the big three infectious diseases (HIV/AIDS, malaria and tuberculosis), which are generally less neglected. NTDs affect more than 1 billion people worldwide (World Health Organization 2012).

For some NTDs, there are treatments but no vaccines: for example, praziquantel is an effective treatment for schistosomiasis. For other NTDs, such as dengue, there are neither treatments nor vaccines.

Since there has been little assessment of this area, current cost-effectiveness estimates are very speculative. However, they indicate that research into NTDs may be several times more effective than other global health interventions.