High altitude research is comparatively a recent development. With the notable exceptions of entomology, botany and perhaps some aspects of human acclimatization, our knowledge of high altitude environment is extremely scanty. There is at present no comprehensive handbook on the general ecology of highlands. This book aims at providing such a text for the use of the general scientist, engineer, biologist and university students. It summarizes and critically reviews current developments and focusses atten- tion on urgent problems of highland ecology needing future studies. This book has grown out of our explorations and experiences in the highlands of Asia and South America. The results of explorations of the high altitude plants and insects on the Himalaya, Alai-Pamirs, Central Tien Shan and Caucasus by one of us (MSM), discussed in earlier publications, are reviewed here in the light of recent advances. Many years' experience of teaching and research in the University of Sucre (3400 m) and studies at Potosi (4000 m), La Paz and Chacaltaya (5000 m) in Bolivia by the second author (LEG) cover problems in physical chemistry, meteorology, engineer- ing and other physical aspects of highland environments.