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On December 29, 1959, physicist Richard Feynman delivered at Caltech the lecture "There's Plenty of Room at the Bottom", in which he envisioned the possibility of manipulating matter at the atomic scale. It is considered the founding lecture of nanotechnology, a science that has transformed medicine, electronics and materials.

On December 29, 1890, soldiers of the US Army's 7th Cavalry massacred between 250 and 350 Lakota Sioux Indians, including women and children, at Wounded Knee Creek, South Dakota. The Wounded Knee Massacre was the last major clash between the American army and indigenous peoples and symbolised the definitive crushing of Native resistance.

On December 29, 1170, four knights of King Henry II of England murdered Archbishop of Canterbury Thomas Becket in his own cathedral. Becket, who had been the king's close friend, had clashed with him over the Church's independence from royal power. The crime shocked Europe; Becket was canonised in 1173 and Canterbury Cathedral became a pilgrimage site.