Over the past 150 years National Hydrological Associations (NHAs) have been established in many countries. Hydrology has developed within many different contexts, as is reflected in the diverse nature of the NHAs that exist. Some NHAs have developed within a governmental context, while others owe their existence to the efforts by individual hydrologists. Their common objective is the promotion of the science and practice of hydrology, but their range of activities is very wide. On many occasions the International Association of Hydrological Sciences (IAHS) has collaborated with such Associations and has proposed that much could be gained if NHAs were to be in contact with each other, as well as with IAHS. From this arose the idea of establishing a Network of NHAs. An Agreement for the establishment of the Network was signed in Gothenburg in July 2013. Its Second General Assembly was held in Prague in July 2015.