Innerste, in earlier times called the Inste (1805), Inderste (1567), Indistria (1313), Entrista (1065) and Indrista (1013), probably goes back to the Indo-Germanic root oid = turbulent, strong.

The river's source is in the Harz mountains, 4 km (2.5 mi) from the town of Clausthal-Zellerfeld to the southwest at an elevation of 615 m and is called Innerstesprung.

As a small brook, the Innerste flows west and passes a system of lakes, the first of which is called Entensumpf.

A few kilometers further on, the Innerste leaves the Harz Mountains near the town of Langelsheim (204 m) and turns to the Northwest.

About 18 km (11 mi) further on, it flows into the Leine near the town of Sarstedt, south of Hanover, at an elevation of 65 m. Wilhelm Raabe wrote a novelle titled Die Innerste.