High Rhine (German: Hochrhein, pronounced [ˈhoːxˌʁaɪn] ^ⓘ; kilometres 0 to 167 of the Rhine) is the section of the Rhine between Lake Constance (Bodensee) and the city of Basel, flowing in a general east-to-west direction and forming mostly the Germany–Switzerland border. It is the first of four named sections of the Rhine (High Rhine, Upper Rhine, Middle Rhine, Lower Rhine) between Lake Constance and the river delta at the North Sea.

The term High Rhine was introduced by scientists in the 19th century.^{[citation needed]} Above all geologists tried to differentiate the High Rhine (German: Hochrhein) linguistically from the Upper Rhine (French: Rhin Supérieur, German: Oberrhein). Until the 19th century, it was also known as the 'Badisch-Swiss Rhine'. It lends its name to the High Rhine Railway line, which to a great extent follows the river to the north of it.

The High Rhine begins at the outflow of the Rhine from the Untersee (Lower Lake Constance) in Stein am Rhein and turns into the Upper Rhine at the Rhine knee (Rheinknie) in Basel (more precisely at the Middle Bridge). It is marked by Rhine-kilometers 0 to 167, with the measurements beginning at the outflow from the Obersee (Upper Lake Constance) at the Old Rhine Bridge in Konstanz (Constance), although the part between the Upper and Lower Lake Constance is distinguished as the Seerhein (English: Lake Rhine) and the part of Lower Lake Constance through which the Rhine flows is known as the Rheinsee. Therefore, the High Rhine begins at Rhine-kilometer 25.45.

In contrast to the Alpine Rhine (the main tributary of Lake Constance) and Upper Rhine, which both flow mainly in a south-to-north direction, the High Rhine flows mostly from east to west. Between Schaffhausen and the confluence with the Töss, it flows from north to south for about 20 km (12 mi), with a distinct meander at Rheinau. In its eastern portion, the river passes through the Molasse basin (passing south of the Hegau region), while in its western part it traverses the Table Jura before entering the Upper Rhine Plain at Basel, where it turns northwards.

In its western section, the High Rhine mostly marks the border between Germany and Switzerland except in the Swiss canton of Basel-Stadt. In the eastern part, there are several disconnected areas of Switzerland to the north of the river (canton of Schaffhausen and Rafzerfeld of the canton of Zurich). The German enclave of Büsingen am Hochrhein is located on the northern bank of the High Rhine, surrounded by Swiss territory.

Apart from many creeks, larger tributaries of the High Rhine are, in the order of their confluences, the Biber, Durach, Thur, Töss, Glatt, Wutach, Aare, Alb, Murg, Sissle, Wehra, Ergolz and Birs. The High Rhine's drainage basin measures 24,900 km² (9,600 sq mi).

With 557 cubic metres per second (19,700 cu ft/s), the Aare has a larger discharge than the Rhine (439 cubic metres per second (15,500 cu ft/s)). From a hydrological point of view, therefore, the Rhine is a tributary of the Aare, not vice versa. The Rhine is, however, generally considered the main stream, because it is slightly longer than the Aare.

The Rhine Falls (Rheinfall), which are the largest plain waterfalls of Europe, are in the municipalities of Neuhausen am Rheinfall and Laufen-Uhwiesen, near the town of Schaffhausen. They are 150 metres (490 ft) wide and 23 metres (75 ft) high. In the winter months, the average water flow is 250 cubic metres per second (8,800 cu ft/s), while in the summer, the average water flow is 600 cubic metres per second (21,000 cu ft/s).