This contribution outlines the genesis and some features of the modern law of international watercourses, especially the principle of reasonable and equitable utilisation and the no-harm rule, as well as the relation between them. It describes and comments on the issue of prior notice of measures planned by watercourse States and on the duty to organise environmental impact assessments. It also considers problems of dispute settlement under the rules of international law, in particular under Article 33 of the 1997 Convention on the Non-navigational Utilisation of International Watercourses which entered into force on 17 August 2014.