Carl Diener (11 December 1862 – 6 January 1928) was an Austrian geographer, geologist and paleontologist.

In 1883 he received his doctorate from the University of Vienna, where his instructors included Eduard Suess and Melchior Neumayr.

He also conducted important research on his numerous travels worldwide — Syria and Lebanon (1885), the Pyrenees (1886), the Himalayas (1892), Svalbard (1893), the Urals and the Caucasus (1897), North America (1901), et al.[1] In 1895, with Wilhelm Heinrich Waagen, he proposed the Anisian Stage (a division of the Middle Triassic) as a replacement for the "Alpine Muschelkalk".

[2] He was an avid mountaineer, and for a number of years was president of the Österreichischer Alpenverein (Austrian Alpine Club).

[1] Diener Creek on Ellesmere Island is named after him, and indirectly the Dienerian substage of the Early Triassic epoch.