Climate change is causing significant mass loss of glaciers in high mountains worldwide. Although glacier systems show a great amount of inherent complexity and variation, there are clear overall trends indicating global glacier recession, which is likely to accelerate in coming decades. Large gaps remain in our understanding and ability to model accurately the key processes and cause-effect relationships driving glacier response to climate change. In addition, a lot of data on glacier mass changes are not available to the public due to national interests concerning water supply.