Political borders rely as much as possible on natural borders, especially those created by mountains and rivers. Even though a river in the sense of a watercourse is a natural feature, a border river primarily becomes a social fact when it acquires a demarcating function. As in Slovenia, this applies ‒ sometimes even more distinctly ‒ to rivers throughout the world and in Europe, where this phenomenon has already been systematically studied. This article systematically reviews border rivers for the entire planet, individual continents, and individual countries, highlighting those where the share of river borders is the greatest in relation to the total length of the country’s borders. Border rivers are analyzed with regard to their dimensions, degree of artificial transformation, and important geographical features along and on them, such as major towns, bridges, hydroelectric plants, reservoirs, and river ports. They are categorized with regard to the size of the country, basic natural features (upper, middle, and lower flow), climate zones, and density of settlement along them. The current and historically best-known border disputes along rivers throughout the world are also examined, in which a border river may have only been the scene of events or the object in an international dispute that led to armed conflict.