The Hindu Kush Himalayas (HKH) is a mountain system of extremes with great influence over the Asian continent. The system stretches 3,500 km over eight countries, from Afghanistan in the west to Myanmar in the east. It is the world’s largest and highest mountain system, with more than 30 peaks measuring over 7,600 m. It is also the youngest mountain system on Earth and still tectonically active. The HKH region is characterized by fragile bedrock, steep slopes, and a high rate of surface erosion. Its superlative dimensions give it enormous influence over the climate of Asia. The HKH mountains block the monsoon from the south as well as extremely cold air blowing from the north. Consequently, the southern slopes and valleys host some of the wettest, greenest mountain ecosystems in the world, particularly in the east, for example the subtropical uplands of Myanmar. In contrast, the northern mountains and Tibetan plateau are generally snowy, much colder, and in some areas dry and nearly devoid of vegetation.