Oscar Johannes Ludwig Eckenstein (9 September 1859 – 8 April 1921) was an English rock climber and mountaineer, and a pioneer in the sport of bouldering.

Inventor of the modern crampon,[1] he was an innovator in climbing technique and mountaineering equipment, and the leader of the first serious expedition to attempt K2.

Eckenstein climbed in the English Lake District with George and Ashley Abraham, though their relationship was not always smooth, and in North Wales with Geoffrey Winthrop Young and J. M. Archer Thomson.

Upon arrival in India, Eckenstein was detained by British authorities for three weeks on suspicion of being a spy, and not allowed to enter Kashmir.

He and Crowley were convinced that Martin Conway was responsible for trying to interfere with their attempt on K2, and only when they threatened to take the matter to the newspapers was Eckenstein released.

The failures were also attributed to sickness (Crowley was suffering the residual effects of malaria), a combination of questionable physical training, personality conflicts, and poor weather conditions – of 68 days spent on K2 (at the time, the record for the longest time spent at such an altitude) only eight provided clear weather.

Eckenstein started the trend toward shorter ice axes with a lighter model measuring 85–86 cm, which could be used single handed.

Initially, this innovation was criticised by well-known climbers of the era, including his nemesis Martin Conway, a prominent member of the Alpine Club.

He was an advocate of guideless climbing in a period when conventional thinking in the Alpine Club called for gentlemen climbers to be led to the top of peaks by paid professional guides.