The centenary of the Anglo-American high altitude expedition to Pikes Peak in 1911 provides an opportunity to look at the development of high altitude physiology before and since then. A watershed event was the publication of La Pression Barométrique by Paul Bert in Paris in 1878. This clearly implicated the low PO2 in the air as the critical variable. A few years later the first high altitude research laboratory was erected on Mont Blanc at an altitude of 4350 m. Shortly thereafter Angelo Mosso from Turin arranged for the Capanna Margherita to be placed at an altitude of 4559 m on the Monte Rosa. This was the site of extensive physiological studies carried out by a burgeoning international high altitude physiology community. This included Nathan Zuntz from Berlin who organized an international expedition to the Alta Vista Hut, altitude 3350 m, on Tenerife, Canary Islands. The Pikes Peak expedition led by J. S. Haldane from Oxford and Y. Henderson from Yale had a classical design with measurements first at sea level, then on the summit, altitude 4300 m, for five weeks, and then back at sea level. Extensive studies of cardiorespiratory physiology were carried out which laid the basis of much of what we know today. More recently the first measurements of human physiology on the summit of Mt. Everest, altitude 8848 m, were made in 1981, a simulated ascent of Everest in a low-pressure chamber took place in 1985, and very recently arterial blood samples were taken near the summit. A dramatic advance has been the discovery of a genetic change in Tibetans with extensive implications for the oxygen transport system. High altitude physiology is one of the most colorful and fast moving areas of environmental physiology.